mm: softdirty: add pgtable_supports_soft_dirty()

Patch series "mm: Add soft-dirty and uffd-wp support for RISC-V", v15.

This patchset adds support for Svrsw60t59b [1] extension which is ratified
now, also add soft dirty and userfaultfd write protect tracking for
RISC-V.

The patches 1 and 2 add macros to allow architectures to define their own
checks if the soft-dirty / uffd_wp PTE bits are available, in other words
for RISC-V, the Svrsw60t59b extension is supported on which device the
kernel is running.  Also patch1-2 are removing "ifdef
CONFIG_MEM_SOFT_DIRTY" "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and "ifdef
CONFIG_PTE_MARKER_UFFD_WP" in favor of checks which if not overridden by
the architecture, no change in behavior is expected.

This patchset has been tested with kselftest mm suite in which soft-dirty,
madv_populate, test_unmerge_uffd_wp, and uffd-unit-tests run and pass, and
no regressions are observed in any of the other tests.


This patch (of 6):

Some platforms can customize the PTE PMD entry soft-dirty bit making it
unavailable even if the architecture provides the resource.

Add an API which architectures can define their specific implementations
to detect if soft-dirty bit is available on which device the kernel is
running.

This patch is removing "ifdef CONFIG_MEM_SOFT_DIRTY" in favor of
pgtable_supports_soft_dirty() checks that defaults to
IS_ENABLED(CONFIG_MEM_SOFT_DIRTY), if not overridden by the architecture,
no change in behavior is expected.

We make sure to never set VM_SOFTDIRTY if !pgtable_supports_soft_dirty(),
so we will never run into VM_SOFTDIRTY checks.

[lorenzo.stoakes@oracle.com: fix VMA selftests]
  Link: https://lkml.kernel.org/r/dac6ddfe-773a-43d5-8f69-021b9ca4d24b@lucifer.local
Link: https://lkml.kernel.org/r/20251113072806.795029-1-zhangchunyan@iscas.ac.cn
Link: https://lkml.kernel.org/r/20251113072806.795029-2-zhangchunyan@iscas.ac.cn
Link: https://github.com/riscv-non-isa/riscv-iommu/pull/543 [1]
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Conor Dooley <conor@kernel.org>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/proc/task_mmu.c

@@ -1584,8 +1584,6 @@ struct clear_refs_private {
 	enum clear_refs_types type;
 };
 
-#ifdef CONFIG_MEM_SOFT_DIRTY
-
 static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
 {
 	struct folio *folio;
@@ -1605,6 +1603,8 @@ static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr,
 static inline void clear_soft_dirty(struct vm_area_struct *vma,
 		unsigned long addr, pte_t *pte)
 {
+	if (!pgtable_supports_soft_dirty())
+		return;
 	/*
 	 * The soft-dirty tracker uses #PF-s to catch writes
 	 * to pages, so write-protect the pte as well. See the
@@ -1630,19 +1630,16 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
 		set_pte_at(vma->vm_mm, addr, pte, ptent);
 	}
 }
-#else
-static inline void clear_soft_dirty(struct vm_area_struct *vma,
-		unsigned long addr, pte_t *pte)
-{
-}
-#endif
 
-#if defined(CONFIG_MEM_SOFT_DIRTY) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
 static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
 		unsigned long addr, pmd_t *pmdp)
 {
 	pmd_t old, pmd = *pmdp;
 
+	if (!pgtable_supports_soft_dirty())
+		return;
+
 	if (pmd_present(pmd)) {
 		/* See comment in change_huge_pmd() */
 		old = pmdp_invalidate(vma, addr, pmdp);

include/linux/mm.h

@@ -859,6 +859,7 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
 static inline void vm_flags_init(struct vm_area_struct *vma,
 				 vm_flags_t flags)
 {
+	VM_WARN_ON_ONCE(!pgtable_supports_soft_dirty() && (flags & VM_SOFTDIRTY));
 	ACCESS_PRIVATE(vma, __vm_flags) = flags;
 }
 
@@ -870,6 +871,7 @@ static inline void vm_flags_init(struct vm_area_struct *vma,
 static inline void vm_flags_reset(struct vm_area_struct *vma,
 				  vm_flags_t flags)
 {
+	VM_WARN_ON_ONCE(!pgtable_supports_soft_dirty() && (flags & VM_SOFTDIRTY));
 	vma_assert_write_locked(vma);
 	vm_flags_init(vma, flags);
 }
@@ -891,6 +893,7 @@ static inline void vm_flags_set(struct vm_area_struct *vma,
 static inline void vm_flags_clear(struct vm_area_struct *vma,
 				  vm_flags_t flags)
 {
+	VM_WARN_ON_ONCE(!pgtable_supports_soft_dirty() && (flags & VM_SOFTDIRTY));
 	vma_start_write(vma);
 	ACCESS_PRIVATE(vma, __vm_flags) &= ~flags;
 }

include/linux/pgtable.h

@@ -1553,6 +1553,18 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 #define arch_start_context_switch(prev)	do {} while (0)
 #endif
 
+/*
+ * Some platforms can customize the PTE soft-dirty bit making it unavailable
+ * even if the architecture provides the resource.
+ * Adding this API allows architectures to add their own checks for the
+ * devices on which the kernel is running.
+ * Note: When overriding it, please make sure the CONFIG_MEM_SOFT_DIRTY
+ * is part of this macro.
+ */
+#ifndef pgtable_supports_soft_dirty
+#define pgtable_supports_soft_dirty()	IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)
+#endif
+
 #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
 #ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
 static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)

mm/debug_vm_pgtable.c

@@ -704,7 +704,7 @@ static void __init pte_soft_dirty_tests(struct pgtable_debug_args *args)
 {
 	pte_t pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
 
-	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+	if (!pgtable_supports_soft_dirty())
 		return;
 
 	pr_debug("Validating PTE soft dirty\n");
@@ -717,7 +717,7 @@ static void __init pte_swap_soft_dirty_tests(struct pgtable_debug_args *args)
 	pte_t pte;
 	softleaf_t entry;
 
-	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+	if (!pgtable_supports_soft_dirty())
 		return;
 
 	pr_debug("Validating PTE swap soft dirty\n");
@@ -734,7 +734,7 @@ static void __init pmd_soft_dirty_tests(struct pgtable_debug_args *args)
 {
 	pmd_t pmd;
 
-	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+	if (!pgtable_supports_soft_dirty())
 		return;
 
 	if (!has_transparent_hugepage())
@@ -750,7 +750,7 @@ static void __init pmd_leaf_soft_dirty_tests(struct pgtable_debug_args *args)
 {
 	pmd_t pmd;
 
-	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) ||
+	if (!pgtable_supports_soft_dirty() ||
 	    !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
 		return;
 

mm/huge_memory.c

@@ -2427,12 +2427,13 @@ static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
 
 static pmd_t move_soft_dirty_pmd(pmd_t pmd)
 {
-#ifdef CONFIG_MEM_SOFT_DIRTY
+	if (pgtable_supports_soft_dirty()) {
 		if (unlikely(pmd_is_migration_entry(pmd)))
 			pmd = pmd_swp_mksoft_dirty(pmd);
 		else if (pmd_present(pmd))
 			pmd = pmd_mksoft_dirty(pmd);
-#endif
+	}
+
 	return pmd;
 }
 

mm/internal.h

@@ -1554,7 +1554,7 @@ static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma)
 	 * VM_SOFTDIRTY is defined as 0x0, then !(vm_flags & VM_SOFTDIRTY)
 	 * will be constantly true.
 	 */
-	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+	if (!pgtable_supports_soft_dirty())
 		return false;
 
 	/*

mm/mmap.c

@@ -1448,8 +1448,10 @@ static struct vm_area_struct *__install_special_mapping(
 		return ERR_PTR(-ENOMEM);
 
 	vma_set_range(vma, addr, addr + len, 0);
-	vm_flags_init(vma, (vm_flags | mm->def_flags |
-		      VM_DONTEXPAND | VM_SOFTDIRTY) & ~VM_LOCKED_MASK);
+	vm_flags |= mm->def_flags | VM_DONTEXPAND;
+	if (pgtable_supports_soft_dirty())
+		vm_flags |= VM_SOFTDIRTY;
+	vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
 	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 
 	vma->vm_ops = ops;

mm/mremap.c

@@ -165,12 +165,13 @@ static pte_t move_soft_dirty_pte(pte_t pte)
 	 * Set soft dirty bit so we can notice
 	 * in userspace the ptes were moved.
 	 */
-#ifdef CONFIG_MEM_SOFT_DIRTY
+	if (pgtable_supports_soft_dirty()) {
 		if (pte_present(pte))
 			pte = pte_mksoft_dirty(pte);
 		else
 			pte = pte_swp_mksoft_dirty(pte);
-#endif
+	}
+
 	return pte;
 }
 

mm/userfaultfd.c

@@ -1119,9 +1119,8 @@ static long move_present_ptes(struct mm_struct *mm,
 
 		orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
 		/* Set soft dirty bit so userspace can notice the pte was moved */
-#ifdef CONFIG_MEM_SOFT_DIRTY
+		if (pgtable_supports_soft_dirty())
 			orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
-#endif
 		if (pte_dirty(orig_src_pte))
 			orig_dst_pte = pte_mkdirty(orig_dst_pte);
 		orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);
@@ -1208,9 +1207,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
 	}
 
 	orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
-#ifdef CONFIG_MEM_SOFT_DIRTY
+	if (pgtable_supports_soft_dirty())
 		orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
-#endif
 	set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
 	double_pt_unlock(dst_ptl, src_ptl);
 

mm/vma.c

@@ -2559,6 +2559,7 @@ static void __mmap_complete(struct mmap_state *map, struct vm_area_struct *vma)
 	 * then new mapped in-place (which must be aimed as
 	 * a completely new data area).
 	 */
+	if (pgtable_supports_soft_dirty())
 		vm_flags_set(vma, VM_SOFTDIRTY);
 
 	vma_set_page_prot(vma);
@@ -2864,6 +2865,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	mm->data_vm += len >> PAGE_SHIFT;
 	if (vm_flags & VM_LOCKED)
 		mm->locked_vm += (len >> PAGE_SHIFT);
+	if (pgtable_supports_soft_dirty())
 		vm_flags_set(vma, VM_SOFTDIRTY);
 	return 0;
 

mm/vma_exec.c

@@ -107,6 +107,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
 int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
 			  unsigned long *top_mem_p)
 {
+	unsigned long flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
 	int err;
 	struct vm_area_struct *vma = vm_area_alloc(mm);
 
@@ -137,7 +138,9 @@ int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
 	BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
 	vma->vm_end = STACK_TOP_MAX;
 	vma->vm_start = vma->vm_end - PAGE_SIZE;
-	vm_flags_init(vma, VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP);
+	if (pgtable_supports_soft_dirty())
+		flags |= VM_SOFTDIRTY;
+	vm_flags_init(vma, flags);
 	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 
 	err = insert_vm_struct(mm, vma);

tools/testing/vma/vma_internal.h

@@ -212,6 +212,8 @@ typedef __bitwise unsigned int vm_fault_t;
 
 #define ASSERT_EXCLUSIVE_WRITER(x)
 
+#define pgtable_supports_soft_dirty() 1
+
 /**
  * swap - swap values of @a and @b
  * @a: first value