mirror of https://github.com/torvalds/linux.git
30 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Suren Baghdasaryan
|
3104138517 |
mm: make vma cache SLAB_TYPESAFE_BY_RCU
To enable SLAB_TYPESAFE_BY_RCU for vma cache we need to ensure that object reuse before RCU grace period is over will be detected by lock_vma_under_rcu(). Current checks are sufficient as long as vma is detached before it is freed. The only place this is not currently happening is in exit_mmap(). Add the missing vma_mark_detached() in exit_mmap(). Another issue which might trick lock_vma_under_rcu() during vma reuse is vm_area_dup(), which copies the entire content of the vma into a new one, overriding new vma's vm_refcnt and temporarily making it appear as attached. This might trick a racing lock_vma_under_rcu() to operate on a reused vma if it found the vma before it got reused. To prevent this situation, we should ensure that vm_refcnt stays at detached state (0) when it is copied and advances to attached state only after it is added into the vma tree. Introduce vm_area_init_from() which preserves new vma's vm_refcnt and use it in vm_area_dup(). Since all vmas are in detached state with no current readers when they are freed, lock_vma_under_rcu() will not be able to take vm_refcnt after vma got detached even if vma is reused. vma_mark_attached() in modified to include a release fence to ensure all stores to the vma happen before vm_refcnt gets initialized. Finally, make vm_area_cachep SLAB_TYPESAFE_BY_RCU. This will facilitate vm_area_struct reuse and will minimize the number of call_rcu() calls. [surenb@google.com: remove atomic_set_release() usage in tools/] Link: https://lkml.kernel.org/r/20250217054351.2973666-1-surenb@google.com Link: https://lkml.kernel.org/r/20250213224655.1680278-18-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Tested-by: Shivank Garg <shivankg@amd.com> Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Klara Modin <klarasmodin@gmail.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Sourav Panda <souravpanda@google.com> Cc: Wei Yang <richard.weiyang@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Suren Baghdasaryan
|
6bef4c2f97 |
mm: move lesser used vma_area_struct members into the last cacheline
Move several vma_area_struct members which are rarely or never used during
page fault handling into the last cacheline to better pack vm_area_struct.
As a result vm_area_struct will fit into 3 as opposed to 4 cachelines.
New typical vm_area_struct layout:
struct vm_area_struct {
union {
struct {
long unsigned int vm_start; /* 0 8 */
long unsigned int vm_end; /* 8 8 */
}; /* 0 16 */
freeptr_t vm_freeptr; /* 0 8 */
}; /* 0 16 */
struct mm_struct * vm_mm; /* 16 8 */
pgprot_t vm_page_prot; /* 24 8 */
union {
const vm_flags_t vm_flags; /* 32 8 */
vm_flags_t __vm_flags; /* 32 8 */
}; /* 32 8 */
unsigned int vm_lock_seq; /* 40 4 */
/* XXX 4 bytes hole, try to pack */
struct list_head anon_vma_chain; /* 48 16 */
/* --- cacheline 1 boundary (64 bytes) --- */
struct anon_vma * anon_vma; /* 64 8 */
const struct vm_operations_struct * vm_ops; /* 72 8 */
long unsigned int vm_pgoff; /* 80 8 */
struct file * vm_file; /* 88 8 */
void * vm_private_data; /* 96 8 */
atomic_long_t swap_readahead_info; /* 104 8 */
struct mempolicy * vm_policy; /* 112 8 */
struct vma_numab_state * numab_state; /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
refcount_t vm_refcnt (__aligned__(64)); /* 128 4 */
/* XXX 4 bytes hole, try to pack */
struct {
struct rb_node rb (__aligned__(8)); /* 136 24 */
long unsigned int rb_subtree_last; /* 160 8 */
} __attribute__((__aligned__(8))) shared; /* 136 32 */
struct anon_vma_name * anon_name; /* 168 8 */
struct vm_userfaultfd_ctx vm_userfaultfd_ctx; /* 176 8 */
/* size: 192, cachelines: 3, members: 18 */
/* sum members: 176, holes: 2, sum holes: 8 */
/* padding: 8 */
/* forced alignments: 2, forced holes: 1, sum forced holes: 4 */
} __attribute__((__aligned__(64)));
Memory consumption per 1000 VMAs becomes 48 pages:
slabinfo after vm_area_struct changes:
<name> ... <objsize> <objperslab> <pagesperslab> : ...
vm_area_struct ... 192 42 2 : ...
Link: https://lkml.kernel.org/r/20250213224655.1680278-14-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Suren Baghdasaryan
|
f35ab95ca0 |
mm: replace vm_lock and detached flag with a reference count
rw_semaphore is a sizable structure of 40 bytes and consumes considerable space for each vm_area_struct. However vma_lock has two important specifics which can be used to replace rw_semaphore with a simpler structure: 1. Readers never wait. They try to take the vma_lock and fall back to mmap_lock if that fails. 2. Only one writer at a time will ever try to write-lock a vma_lock because writers first take mmap_lock in write mode. Because of these requirements, full rw_semaphore functionality is not needed and we can replace rw_semaphore and the vma->detached flag with a refcount (vm_refcnt). When vma is in detached state, vm_refcnt is 0 and only a call to vma_mark_attached() can take it out of this state. Note that unlike before, now we enforce both vma_mark_attached() and vma_mark_detached() to be done only after vma has been write-locked. vma_mark_attached() changes vm_refcnt to 1 to indicate that it has been attached to the vma tree. When a reader takes read lock, it increments vm_refcnt, unless the top usable bit of vm_refcnt (0x40000000) is set, indicating presence of a writer. When writer takes write lock, it sets the top usable bit to indicate its presence. If there are readers, writer will wait using newly introduced mm->vma_writer_wait. Since all writers take mmap_lock in write mode first, there can be only one writer at a time. The last reader to release the lock will signal the writer to wake up. refcount might overflow if there are many competing readers, in which case read-locking will fail. Readers are expected to handle such failures. In summary: 1. all readers increment the vm_refcnt; 2. writer sets top usable (writer) bit of vm_refcnt; 3. readers cannot increment the vm_refcnt if the writer bit is set; 4. in the presence of readers, writer must wait for the vm_refcnt to drop to 1 (plus the VMA_LOCK_OFFSET writer bit), indicating an attached vma with no readers; 5. vm_refcnt overflow is handled by the readers. While this vm_lock replacement does not yet result in a smaller vm_area_struct (it stays at 256 bytes due to cacheline alignment), it allows for further size optimization by structure member regrouping to bring the size of vm_area_struct below 192 bytes. [surenb@google.com: fix a crash due to vma_end_read() that should have been removed] Link: https://lkml.kernel.org/r/20250220200208.323769-1-surenb@google.com Link: https://lkml.kernel.org/r/20250213224655.1680278-13-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Matthew Wilcox <willy@infradead.org> Tested-by: Shivank Garg <shivankg@amd.com> Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Klara Modin <klarasmodin@gmail.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Sourav Panda <souravpanda@google.com> Cc: Wei Yang <richard.weiyang@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Suren Baghdasaryan
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55e50223bf |
mm: introduce vma_iter_store_attached() to use with attached vmas
vma_iter_store() functions can be used both when adding a new vma and when updating an existing one. However for existing ones we do not need to mark them attached as they are already marked that way. With vma->detached being a separate flag, double-marking a vmas as attached or detached is not an issue because the flag will simply be overwritten with the same value. However once we fold this flag into the refcount later in this series, re-attaching or re-detaching a vma becomes an issue since these operations will be incrementing/decrementing a refcount. Introduce vma_iter_store_new() and vma_iter_store_overwrite() to replace vma_iter_store() and avoid re-attaching a vma during vma update. Add assertions in vma_mark_attached()/vma_mark_detached() to catch invalid usage. Update vma tests to check for vma detached state correctness. Link: https://lkml.kernel.org/r/20250213224655.1680278-5-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Tested-by: Shivank Garg <shivankg@amd.com> Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Klara Modin <klarasmodin@gmail.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Sourav Panda <souravpanda@google.com> Cc: Wei Yang <richard.weiyang@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Suren Baghdasaryan
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8ef95d8f15 |
mm: mark vma as detached until it's added into vma tree
Current implementation does not set detached flag when a VMA is first allocated. This does not represent the real state of the VMA, which is detached until it is added into mm's VMA tree. Fix this by marking new VMAs as detached and resetting detached flag only after VMA is added into a tree. Introduce vma_mark_attached() to make the API more readable and to simplify possible future cleanup when vma->vm_mm might be used to indicate detached vma and vma_mark_attached() will need an additional mm parameter. Link: https://lkml.kernel.org/r/20250213224655.1680278-4-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com> Tested-by: Shivank Garg <shivankg@amd.com> Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Klara Modin <klarasmodin@gmail.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Sourav Panda <souravpanda@google.com> Cc: Wei Yang <richard.weiyang@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Suren Baghdasaryan
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7b6218ae12 |
mm: move per-vma lock into vm_area_struct
Back when per-vma locks were introduces, vm_lock was moved out of
vm_area_struct in [1] because of the performance regression caused by
false cacheline sharing. Recent investigation [2] revealed that the
regressions is limited to a rather old Broadwell microarchitecture and
even there it can be mitigated by disabling adjacent cacheline
prefetching, see [3].
Splitting single logical structure into multiple ones leads to more
complicated management, extra pointer dereferences and overall less
maintainable code. When that split-away part is a lock, it complicates
things even further. With no performance benefits, there are no reasons
for this split. Merging the vm_lock back into vm_area_struct also allows
vm_area_struct to use SLAB_TYPESAFE_BY_RCU later in this patchset. Move
vm_lock back into vm_area_struct, aligning it at the cacheline boundary
and changing the cache to be cacheline-aligned as well. With kernel
compiled using defconfig, this causes VMA memory consumption to grow from
160 (vm_area_struct) + 40 (vm_lock) bytes to 256 bytes:
slabinfo before:
<name> ... <objsize> <objperslab> <pagesperslab> : ...
vma_lock ... 40 102 1 : ...
vm_area_struct ... 160 51 2 : ...
slabinfo after moving vm_lock:
<name> ... <objsize> <objperslab> <pagesperslab> : ...
vm_area_struct ... 256 32 2 : ...
Aggregate VMA memory consumption per 1000 VMAs grows from 50 to 64 pages,
which is 5.5MB per 100000 VMAs. Note that the size of this structure is
dependent on the kernel configuration and typically the original size is
higher than 160 bytes. Therefore these calculations are close to the
worst case scenario. A more realistic vm_area_struct usage before this
change is:
<name> ... <objsize> <objperslab> <pagesperslab> : ...
vma_lock ... 40 102 1 : ...
vm_area_struct ... 176 46 2 : ...
Aggregate VMA memory consumption per 1000 VMAs grows from 54 to 64 pages,
which is 3.9MB per 100000 VMAs. This memory consumption growth can be
addressed later by optimizing the vm_lock.
[1] https://lore.kernel.org/all/20230227173632.3292573-34-surenb@google.com/
[2] https://lore.kernel.org/all/ZsQyI%2F087V34JoIt@xsang-OptiPlex-9020/
[3] https://lore.kernel.org/all/CAJuCfpEisU8Lfe96AYJDZ+OM4NoPmnw9bP53cT_kbfP_pR+-2g@mail.gmail.com/
Link: https://lkml.kernel.org/r/20250213224655.1680278-3-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Lorenzo Stoakes
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c372473a54 |
mm: completely abstract unnecessary adj_start calculation
The adj_start calculation has been a constant source of confusion in the
VMA merge code.
There are two cases to consider, one where we adjust the start of the
vmg->middle VMA (i.e. the vmg->__adjust_middle_start merge flag is set),
in which case adj_start is calculated as:
(1) adj_start = vmg->end - vmg->middle->vm_start
And the case where we adjust the start of the vmg->next VMA (i.e. the
vmg->__adjust_next_start merge flag is set), in which case adj_start is
calculated as:
(2) adj_start = -(vmg->middle->vm_end - vmg->end)
We apply (1) thusly:
vmg->middle->vm_start =
vmg->middle->vm_start + vmg->end - vmg->middle->vm_start
Which simplifies to:
vmg->middle->vm_start = vmg->end
Similarly, we apply (2) as:
vmg->next->vm_start =
vmg->next->vm_start + -(vmg->middle->vm_end - vmg->end)
Noting that for these VMAs to be mergeable vmg->middle->vm_end ==
vmg->next->vm_start and so this simplifies to:
vmg->next->vm_start =
vmg->next->vm_start + -(vmg->next->vm_start - vmg->end)
Which simplifies to:
vmg->next->vm_start = vmg->end
Therefore in each case, we simply need to adjust the start of the VMA to
vmg->end (!) and can do away with this adj_start calculation. The only
caveat is that we must ensure we update the vm_pgoff field correctly.
We therefore abstract this entire calculation to a new function
vmg_adjust_set_range() which performs this calculation and sets the
adjusted VMA's new range using the general vma_set_range() function.
We also must update vma_adjust_trans_huge() which expects the
now-abstracted adj_start parameter. It turns out this is wholly
unnecessary.
In vma_adjust_trans_huge() the relevant code is:
if (adjust_next > 0) {
struct vm_area_struct *next = find_vma(vma->vm_mm, vma->vm_end);
unsigned long nstart = next->vm_start;
nstart += adjust_next;
split_huge_pmd_if_needed(next, nstart);
}
The only case where this is relevant is when vmg->__adjust_middle_start is
specified (in which case adj_next would have been positive), i.e. the one
in which the vma specified is vmg->prev and this the sought 'next' VMA
would be vmg->middle.
We can therefore eliminate the find_vma() invocation altogether and simply
provide the vmg->middle VMA in this instance, or NULL otherwise.
Again we have an adj_next offset calculation:
next->vm_start + vmg->end - vmg->middle->vm_start
Where next == vmg->middle this simplifies to vmg->end as previously
demonstrated.
Therefore nstart is equal to vmg->end, which is already passed to
vma_adjust_trans_huge() via the 'end' parameter and so this code (rather
delightfully) simplifies to:
if (next)
split_huge_pmd_if_needed(next, end);
With these changes in place, it becomes silly for commit_merge() to return
vmg->target, as it is always the same and threaded through vmg, so we
finally change commit_merge() to return an error value once again.
This patch has no change in functional behaviour.
Link: https://lkml.kernel.org/r/7bce2cd4b5afb56211822835d145471280c3dccc.1738326519.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Lorenzo Stoakes
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fe3e9cf0d7 |
mm: eliminate adj_start parameter from commit_merge()
Introduce internal vmg->__adjust_middle_start and vmg->__adjust_next_start merge flags, enabling us to indicate to commit_merge() that we are performing a merge which either spans only part of vmg->middle, or part of vmg->next respectively. In the former instance, we change the start of vmg->middle to match the attributes of vmg->prev, without spanning all of vmg->middle. This implies that vmg->prev->vm_end and vmg->middle->vm_start are both increased to form the new merged VMA (vmg->prev) and the new subsequent VMA (vmg->middle). In the latter case, we change the end of vmg->middle to match the attributes of vmg->next, without spanning all of vmg->next. This implies that vmg->middle->vm_end and vmg->next->vm_start are both decreased to form the new merged VMA (vmg->next) and the new prior VMA (vmg->middle). Since we now have a stable set of prev, middle, next VMAs threaded through vmg and with these flags set know what is happening, we can perform the calculation in commit_merge() instead. This allows us to drop the confusing adj_start parameter and instead pass semantic information to commit_merge(). In the latter case the -(middle->vm_end - start) calculation becomes -(middle->vm-end - vmg->end), however this is correct as vmg->end is set to the start parameter. This is because in this case (rather confusingly), we manipulate vmg->middle, but ultimately return vmg->next, whose range will be correctly specified. At this point vmg->start, end is the new range for the prior VMA rather than the merged one. This patch has no change in functional behaviour. Link: https://lkml.kernel.org/r/bcec0cd980b373a5eb02236cb033034ce1effe42.1738326519.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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6ab2d9c7c6 |
mm: further refactor commit_merge()
The current VMA merge mechanism contains a number of confusing mechanisms around removal of VMAs on merge and the shrinking of the VMA adjacent to vma->target in the case of merges which result in a partial merge with that adjacent VMA. Since we now have a STABLE set of VMAs - prev, middle, next - we are now able to have the caller of commit_merge() explicitly tell us which VMAs need deleting, using newly introduced internal VMA merge flags. Doing so allows us to embed this state within the VMG and remove the confusing remove, remove2 parameters from commit_merge(). We additionally are able to eliminate the highly confusing and misleading 'expanded' parameter - a parameter that in reality refers to whether or not the return VMA is the target one or the one immediately adjacent. We can infer which is the case from whether or not the adj_start parameter is negative. This also allows us to simplify further logic around iterator configuration and VMA iterator stores. Doing so means we can also eliminate the adjust parameter, as we are able to infer which VMA ought to be adjusted from adj_start - a positive value implies we adjust the start of 'middle', a negative one implies we adjust the start of 'next'. We are then able to have commit_merge() explicitly return the target VMA, or NULL on inability to pre-allocate memory. Errors were previously filtered so behaviour does not change. We additionally move from the slightly odd use of a bitwise-flag enum vmg->merge_flags field to vmg bitfields. This patch has no change in functional behaviour. Link: https://lkml.kernel.org/r/7bf2ed24af68aac18672b7acebbd9102f48c5b03.1738326519.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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3a75ccba04 |
mm: simplify vma merge structure and expand comments
Patch series "mm: further simplify VMA merge operation", v3.
While significant efforts have been made to improve the VMA merge
operation, there remains remnants of the bad (or rather confusing) old
days, which make the code difficult to understand, more bug prone and thus
harder to modify.
This series attempts to significantly improve matters in a number of
respects - with a focus on simplifying the commit_merge() function which
actually actions the merge operation - and importantly, adjusting the two
most confusing merge cases - those in which we 'adjust' the VMA
immediately adjacent to the one being merged.
One source of confusion are the VMAs being threaded through the operation
themselves - vmg->prev, vmg->vma and vmg->next.
At the start of the operation, vmg->vma is either NULL if a new VMA is
propose to be added, or if not then a pointer to an existing VMA being
modified, and prev/next are (perhaps not present) VMAs sat immediately
before and after the range specified in vmg->start, end, respectively.
However, during the VMA merge operation, we change vmg->start, end and
pgoff to span the newly merged range and vmg->vma to either be:
a. The ultimately returned VMA (in most cases) or b. A VMA which we will
manipulate, but ultimately instead return vmg->next.
Case b. especially here is confusing for somebody reading this code, but
the fact we update this state, along with vmg->start, end, pgoff only
makes matters worse.
We simplify things by replacing vmg->vma with vmg->middle and never
changing it - this is always either NULL (for a new VMA) or the VMA being
modified between vmg->prev and vmg->next.
We further simplify by placing the merged VMA in a new vmg->target field -
whether case b. above is the case or not. The reader of the code can now
simply rely on vmg->middle being the middle VMA and vmg->target being the
ultimately merged VMA.
We additionally tackle the confusing cases where we 'adjust' VMAs other
than the one we ultimately return as the merged VMA (this includes case b.
above). These are:
(1)
merge
<----------->
|------||--------| |------------|---|
| prev || middle | -> | target | m |
|------||--------| |------------|---|
In which case middle must be adjusted so middle->vm_start is increased as
well as performing the merge.
(2) (equivalent to case b. above)
<------------->
|---------||------| |---|-------------|
| middle || next | -> | m | target |
|---------||------| |---|-------------|
In which case next must be adjusted so next->vm_start is decreased as well
as performing the merge.
This cases have previously been performed by calculating and passing
around a dubious and confusing 'adj_start' parameter along side a pointer
to an 'adjust' VMA indicating which VMA requires additional adjustment
(middle in case 1 and next in case 2).
With the VMG structure in place we are able to avoid this by simply
setting a merge flag to describe each case:
(1) Sets the vmg->__adjust_middle_start flag
(2) Sets the vmg->__adjust_next_start flag
By doing so it turns out we can vastly simplify the logic and calculate
what is required to perform the operation.
Taken together the refactorings make it far easier to understand what is
being done even in these more confusing cases, make the code far more
maintainable, debuggable, and testable, providing more internal state
indicating what is happening in the merge operation.
The changes have no functional net impact on the merge operation and
everything should still behave as it did before.
This patch (of 5):
The merge code, while much improved, still has a number of points of
confusion. As part of a broader series cleaning this up to make this more
maintainable, we start by addressing some confusion around
vma_merge_struct fields.
So far, the caller either provides no vmg->vma (a new VMA) or supplies the
existing VMA which is being altered, setting vmg->start,end,pgoff to the
proposed VMA dimensions.
vmg->vma is then updated, as are vmg->start,end,pgoff as the merge process
proceeds and the appropriate merge strategy is determined.
This is rather confusing, as vmg->vma starts off as the 'middle' VMA
between vmg->prev,next, but becomes the 'target' VMA, except in one
specific edge case (merge next, shrink middle).
Int his patch we introduce vmg->middle to describe the VMA that is between
vmg->prev and vmg->next, and does NOT change during the merge operation.
We replace vmg->vma with vmg->target, and use this only during the merge
operation itself.
Aside from the merge right, shrink middle case, this becomes the VMA that
forms the basis of the VMA that is returned. This edge case can be
addressed in a future commit.
We also add a number of comments to explain what is going on.
Finally, we adjust the ASCII diagrams showing each merge case in
vma_merge_existing_range() to be clearer - the arrow range previously
showed the vmg->start, end spanned area, but it is clearer to change this
to show the final merged VMA.
This patch has no change in functional behaviour.
Link: https://lkml.kernel.org/r/cover.1738326519.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/4dfe60f1419d55e5d0516f56349695d73a57184c.1738326519.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Suren Baghdasaryan
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cf929a2863 |
tools: add VM_WARN_ON_VMG definition
vma tests compilation yields the following error: vma.c:732:9: error: implicit declaration of function ‘VM_WARN_ON_VMG’ Fix it by adding missing VM_WARN_ON_VMG() definition. Link: https://lkml.kernel.org/r/20250116181538.759469-1-surenb@google.com Fixes: e3a7ae85f87c ("mm/debug: prefer VM_WARN_ON_VMG() to report VMG debug warnings") Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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f8d4a6cabb |
mm: make mmap_region() internal
Now that we have removed the one user of mmap_region() outside of mm, make it internal and add it to vma.c so it can be userland tested. This ensures that all external memory mappings are performed using the appropriate interfaces and allows us to modify memory mapping logic as we see fit. Additionally expand test stubs to allow for the mmap_region() code to compile and be userland testable. Link: https://lkml.kernel.org/r/de5a3c574d35c26237edf20a1d8652d7305709c9.1735819274.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Jann Horn <jannh@google.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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7e8c8fd348 |
tools: testing: add simple __mmap_region() userland test
Introduce demonstrative, basic, __mmap_region() test upon which we can base further work upon moving forwards. This simply asserts that mappings can be made and merges occur as expected. As part of this change, fix the security_vm_enough_memory_mm() stub which was previously incorrectly implemented. Link: https://lkml.kernel.org/r/20241213162409.41498-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Jann Horn <jannh@google.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Suren Baghdasaryan
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e5e7fb278e |
mm: convert mm_lock_seq to a proper seqcount
Convert mm_lock_seq to be seqcount_t and change all mmap_write_lock variants to increment it, in-line with the usual seqcount usage pattern. This lets us check whether the mmap_lock is write-locked by checking mm_lock_seq.sequence counter (odd=locked, even=unlocked). This will be used when implementing mmap_lock speculation functions. As a result vm_lock_seq is also change to be unsigned to match the type of mm_lock_seq.sequence. Link: https://lkml.kernel.org/r/20241122174416.1367052-2-surenb@google.com Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hillf Danton <hdanton@sina.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mateusz Guzik <mjguzik@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Paul E. McKenney <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Sourav Panda <souravpanda@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Wei Yang <richard.weiyang@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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bef5418d1f |
mm/vma: move __vm_munmap() to mm/vma.c
This was arbitrarily left in mmap.c it makes no sense being there, move it to vma.c to render it testable. Link: https://lkml.kernel.org/r/5e5e81807c54dfbe363edb2d431eb3d7a37fcdba.1733248985.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <kees@kernel.org> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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a9d1f3f2d7 |
mm/vma: move stack expansion logic to mm/vma.c
We build on previous work making expand_downwards() an entirely internal function. This logic is subtle and so it is highly useful to get it into vma.c so we can then userland unit test. We must additionally move acct_stack_growth() to vma.c as it is a helper function used by both expand_downwards() and expand_upwards(). We are also then able to mark anon_vma_interval_tree_pre_update_vma() and anon_vma_interval_tree_post_update_vma() static as these are no longer used by anything else. Link: https://lkml.kernel.org/r/0feb104eff85922019d4fb29280f3afb130c5204.1733248985.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <kees@kernel.org> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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c7c643d985 |
mm/vma: move unmapped_area() internals to mm/vma.c
We want to be able to unit test the unmapped area logic, so move it to mm/vma.c. The wrappers which invoke this remain in place in mm/mmap.c. In addition, naturally, update the existing test code to enable this to be compiled in userland. Link: https://lkml.kernel.org/r/53a57a52a64ea54e9d129d2e2abca3a538022379.1733248985.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <kees@kernel.org> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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7d344babac |
mm/vma: move brk() internals to mm/vma.c
Patch series "mm/vma: make more mmap logic userland testable".
This series carries on the work started in previous series and
continued in commit
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Suren Baghdasaryan
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4bbb6df62c |
tools: fix atomic_set() definition to set the value correctly
Currently vma test is failing because of the new vma_assert_attached()
assertion. The check is failing because previous refcount_set() inside
vma_mark_attached() is a NoOp. Fix the definition of atomic_set() to
correctly set the value of the atomic.
Link: https://lkml.kernel.org/r/20241227222220.1726384-1-surenb@google.com
Fixes:
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Lorenzo Stoakes
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c14f8046cd |
tools: testing: add additional vma_internal.h stubs
Patch series "fix error handling in mmap_region() and refactor", v3. The mmap_region() function is somewhat terrifying, with spaghetti-like control flow and numerous means by which issues can arise and incomplete state, memory leaks and other unpleasantness can occur. This series goes to great lengths to simplify how mmap_region() works and to avoid unwinding errors late on in the process of setting up the VMA for the new mapping, and equally avoids such operations occurring while the VMA is in an inconsistent state. This series builds on the previously submitted hotfix patches (see link to v2 below) which addresses the most critical issues around mmap_region(), and further works to improve mmap_region() complexity, stability, and testability. This series moves the code to mm/vma.c to render it userland testable, refactors and simplifies it into smaller functions that are significantly more readable. It additionally avoids performing an attempt at a second merge mid-way through allocating a new VMA, a dubious proposition at best and one that is highly subject to subtle bugs. Rather than do this, we simply note that we ought to retry the merge and do this as a final step. This patch (of 3): Add some additional vma_internal.h stubs in preparation for __mmap_region() being moved to mm/vma.c. Without these the move would result in the tests no longer compiling. Link: https://lkml.kernel.org/r/cover.1729858176.git.lorenzo.stoakes@oracle.com Link: https://lkml.kernel.org/r/74b27e159e261d2ac1fe66a130edad1d61fdc176.1729858176.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Jann Horn <jannh@google.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Xu <peterx@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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7146de5ff5 |
tools: testing: fix phys_addr_t size on 64-bit systems
The phys_addr_t size is predicated on whether CONFIG_PHYS_ADDR_T_64BIT is
set or not.
In the VMA tests, virt_to_phys() from tools/include/linux casts a volatile
void * pointer to phys_addr_t, if CONFIG_PHYS_ADDR_T_64BIT is not set,
this will be 32-bit and trigger a warning.
Obviously this might also lead to truncation, which we would rather avoid.
Fix this by adjusting the generation of generated/bit-length.h to generate
a CONFIG_PHYS_ADDR_T{bits}BIT define.
This does result in the generation of the useless CONFIG_PHYS_ADDR_T_32BIT
define for 32-bit systems, but this should have no effect, and makes
implementation of this easier.
This resolves the issue and the warning.
[lorenzo.stoakes@oracle.com: VMA tests not properly importing bit-length.h]
Link: https://lkml.kernel.org/r/a6183df9-3108-4d59-8128-4fc6c14e22a5@lucifer.local
Link: https://lkml.kernel.org/r/20241017165638.95602-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Lorenzo Stoakes
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e8133a7799 |
tools: testing: add expand-only mode VMA test
Add a test to assert that VMG_FLAG_JUST_EXPAND functions as expected - that is, when the VMA iterator is positioned at the previous VMA and no VMAs proceed it, we observe an expansion with all state as expected. Explicitly place a prior VMA that would otherwise fail this test if the mode were not enabled (as it would traverse to the previous-previous VMA). Link: https://lkml.kernel.org/r/d2f88330254a6448092412bf7dfe077a579ab0dc.1729174352.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Jann Horn <jannh@google.com> Cc: kernel test robot <oliver.sang@intel.com> Cc: Liam R. Howlett <Liam.Howlett@Oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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01c373e9a5 |
mm: rework vm_ops->close() handling on VMA merge
In commit |
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Lorenzo Stoakes
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cc8cb3697a |
mm: refactor vma_merge() into modify-only vma_merge_existing_range()
The existing vma_merge() function is no longer required to handle what were previously referred to as cases 1-3 (i.e. the merging of a new VMA), as this is now handled by vma_merge_new_vma(). Additionally, simplify the convoluted control flow of the original, maintaining identical logic only expressed more clearly and doing away with a complicated set of cases, rather logically examining each possible outcome - merging of both the previous and subsequent VMA, merging of the previous VMA and merging of the subsequent VMA alone. We now utilise the previously implemented commit_merge() function to share logic with vma_expand() de-duplicating code and providing less surface area for bugs and confusion. In order to do so, we adjust this function to accept parameters specific to merging existing ranges. Link: https://lkml.kernel.org/r/2cf6016b7bfcc4965fc3cde10827560c42e4f12c.1725040657.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Mark Brown <broonie@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Bert Karwatzki <spasswolf@web.de> Cc: Jeff Xu <jeffxu@chromium.org> Cc: Jiri Olsa <olsajiri@gmail.com> Cc: Kees Cook <kees@kernel.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Paul Moore <paul@paul-moore.com> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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cacded5e42 |
mm: avoid using vma_merge() for new VMAs
Abstract vma_merge_new_vma() to use vma_merge_struct and rename the resultant function vma_merge_new_range() to be clear what the purpose of this function is - a new VMA is desired in the specified range, and we wish to see if it is possible to 'merge' surrounding VMAs into this range rather than having to allocate a new VMA. Note that this function uses vma_extend() exclusively, so adopts its requirement that the iterator point at or before the gap. We add an assert to this effect. This is as opposed to vma_merge_existing_range(), which will be introduced in a subsequent commit, and provide the same functionality for cases in which we are modifying an existing VMA. In mmap_region() and do_brk_flags() we open code scenarios where we prefer to use vma_expand() rather than invoke a full vma_merge() operation. Abstract this logic and eliminate all of the open-coding, and also use the same logic for all cases where we add new VMAs to, rather than ultimately use vma_merge(), rather use vma_expand(). Doing so removes duplication and simplifies VMA merging in all such cases, laying the ground for us to eliminate the merging of new VMAs in vma_merge() altogether. Also add the ability for the vmg to track state, and able to report errors, allowing for us to differentiate a failed merge from an inability to allocate memory in callers. This makes it far easier to understand what is happening in these cases avoiding confusion, bugs and allowing for future optimisation. Also introduce vma_iter_next_rewind() to allow for retrieval of the next, and (optionally) the prev VMA, rewinding to the start of the previous gap. Introduce are_anon_vmas_compatible() to abstract individual VMA anon_vma comparison for the case of merging on both sides where the anon_vma of the VMA being merged maybe compatible with prev and next, but prev and next's anon_vma's may not be compatible with each other. Finally also introduce can_vma_merge_left() / can_vma_merge_right() to check adjacent VMA compatibility and that they are indeed adjacent. Link: https://lkml.kernel.org/r/49d37c0769b6b9dc03b27fe4d059173832556392.1725040657.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Tested-by: Mark Brown <broonie@kernel.org> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Bert Karwatzki <spasswolf@web.de> Cc: Jeff Xu <jeffxu@chromium.org> Cc: Jiri Olsa <olsajiri@gmail.com> Cc: Kees Cook <kees@kernel.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Paul Moore <paul@paul-moore.com> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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fc21959f74 |
mm: abstract vma_expand() to use vma_merge_struct
The purpose of the vmg is to thread merge state through functions and avoid egregious parameter lists. We expand this to vma_expand(), which is used for a number of merge cases. Accordingly, adjust its callers, mmap_region() and relocate_vma_down(), to use a vmg. An added purpose of this change is the ability in a future commit to perform all new VMA range merging using vma_expand(). Link: https://lkml.kernel.org/r/4bc8c9dbc9ca52452ef8e587b28fe555854ceb38.1725040657.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Mark Brown <broonie@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Bert Karwatzki <spasswolf@web.de> Cc: Jeff Xu <jeffxu@chromium.org> Cc: Jiri Olsa <olsajiri@gmail.com> Cc: Kees Cook <kees@kernel.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Paul Moore <paul@paul-moore.com> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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2f1c6611b0 |
mm: introduce vma_merge_struct and abstract vma_merge(),vma_modify()
Rather than passing around huge numbers of parameters to numerous helper
functions, abstract them into a single struct that we thread through the
operation, the vma_merge_struct ('vmg').
Adjust vma_merge() and vma_modify() to accept this parameter, as well as
predicate functions can_vma_merge_before(), can_vma_merge_after(), and the
vma_modify_...() helper functions.
Also introduce VMG_STATE() and VMG_VMA_STATE() helper macros to allow for
easy vmg declaration.
We additionally remove the requirement that vma_merge() is passed a VMA
object representing the candidate new VMA. Previously it used this to
obtain the mm_struct, file and anon_vma properties of the proposed range
(a rather confusing state of affairs), which are now provided by the vmg
directly.
We also remove the pgoff calculation previously performed vma_modify(),
and instead calculate this in VMG_VMA_STATE() via the vma_pgoff_offset()
helper.
Link: https://lkml.kernel.org/r/a955aad09d81329f6fbeb636b2dd10cde7b73dab.1725040657.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Bert Karwatzki <spasswolf@web.de>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Lorenzo Stoakes
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955db39676 |
tools: add VMA merge tests
Add a variety of VMA merge unit tests to assert that the behaviour of VMA merge is correct at an abstract level and VMAs are merged or not merged as expected. These are intentionally added _before_ we start refactoring vma_merge() in order that we can continually assert correctness throughout the rest of the series. In order to reduce churn going forward, we backport the vma_merge_struct data type to the test code which we introduce and use in a future commit, and add wrappers around the merge new and existing VMA cases. Link: https://lkml.kernel.org/r/1c7a0b43cfad2c511a6b1b52f3507696478ff51a.1725040657.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Mark Brown <broonie@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Bert Karwatzki <spasswolf@web.de> Cc: Jeff Xu <jeffxu@chromium.org> Cc: Jiri Olsa <olsajiri@gmail.com> Cc: Kees Cook <kees@kernel.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Paul Moore <paul@paul-moore.com> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Lorenzo Stoakes
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4e52a60ac5 |
tools: improve vma test Makefile
Patch series "mm: remove vma_merge()", v3. The infamous vma_merge() function has been the cause of a great deal of pain, bugs and confusion for a very long time. It is subtle, contains many corner cases, tries to do far too much and is as a result very fragile. The fact that the function requires there to be a numbering system to cover each possible eventuality with references to each in the many branches of its implementation as to which case you are looking at speaks to all this. Some of this complexity is inherent - unfortunately there is no getting away from the need to figure out precisely how to execute the merge, whether we need to remove VMAs, whether it is safe to do so, what constitutes a mergeable VMA and so on. However, a lot of the complexity is not inherent but instead a product of the function's 'organic' development. Liam has gone to great lengths to improve the situation as a part of his maple tree implementation, greatly improving the readability of the code, and Vlastimil and myself have additionally gone to lengths to try to improve things further. However, with the availability of userland VMA testing, it now becomes possible to perform a rather more significant refactoring while maintaining confidence in its correct operation. An attempt was previously made by Vlastimil [0] to eliminate vma_merge(), however it was rather - brutal - and an astute reader might refer to the date of that patch for insight as to its intent. This series instead divides merge operations into two natural kinds - merges which occur when a NEW vma is being added to the address space, and merges which occur when a vma is being MODIFIED. Happily, the vma_expand() function introduced by Liam, which has the capacity for also deleting a subsequent VMA, covers each of the NEW vma cases. By abstracting the actual final commit of changes to a VMA to its own function, commit_merge() and writing a wrapper around vma_expand() for new VMA cases vma_merge_new_range(), we can avoid having to use vma_merge() for these instances altogether. By doing so we are also able to then de-duplicate all existing merge logic in mmap_region() and do_brk_flags() and have everything invoke this new function, so we universally take the same approach to merging new VMAs. Having done so, we can then completely rework vma_merge() into vma_merge_existing_range() and use this for the instances where a merge is proposed for a region of an existing VMA. This eliminates vma_merge() and its numbered cases and instead divides things into logical cases - merge both, merge left, merge right (the latter 2 being either partial or full merges). The code is heavily annotated with ASCII diagrams and greatly simplified in comparison to the existing vma_merge() function. Having made this change, we take the opportunity to address an issue with merging VMAs possessing a vm_ops->close() hook - commit |
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Lorenzo Stoakes
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9325b8b5a1 |
tools: add skeleton code for userland testing of VMA logic
Establish a new userland VMA unit testing implementation under tools/testing which utilises existing logic providing maple tree support in userland utilising the now-shared code previously exclusive to radix tree testing. This provides fundamental VMA operations whose API is defined in mm/vma.h, while stubbing out superfluous functionality. This exists as a proof-of-concept, with the test implementation functional and sufficient to allow userland compilation of vma.c, but containing only cursory tests to demonstrate basic functionality. Link: https://lkml.kernel.org/r/533ffa2eec771cbe6b387dd049a7f128a53eb616.1722251717.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Tested-by: SeongJae Park <sj@kernel.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Brendan Higgins <brendanhiggins@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Gow <davidgow@google.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Jan Kara <jack@suse.cz> Cc: Kees Cook <kees@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Rae Moar <rmoar@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Pengfei Xu <pengfei.xu@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |