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mm/cma: refuse handing out non-contiguous page ranges 

Let's disallow handing out PFN ranges with non-contiguous pages, so we can
remove the nth-page usage in __cma_alloc(), and so any callers don't have
to worry about that either when wanting to blindly iterate pages.

This is really only a problem in configs with SPARSEMEM but without
SPARSEMEM_VMEMMAP, and only when we would cross memory sections in some
cases.

Will this cause harm?  Probably not, because it's mostly 32bit that does
not support SPARSEMEM_VMEMMAP.  If this ever becomes a problem we could
look into allocating the memmap for the memory sections spanned by a
single CMA region in one go from memblock.

[david@redhat.com: we can have NUMMU configs with SPARSEMEM enabled]
  Link: https://lkml.kernel.org/r/6ec933b1-b3f7-41c0-95d8-e518bb87375e@redhat.com
Link: https://lkml.kernel.org/r/20250901150359.867252-23-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-09-01 17:03:43 +02:00 committed by Andrew Morton
parent b71ddc9ecc
commit 6972706f95
3 changed files with 65 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/mm.h
View File

@ -209,9 +209,15 @@ extern unsigned long sysctl_user_reserve_kbytes;
extern unsigned long sysctl_admin_reserve_kbytes;
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
bool page_range_contiguous(const struct page *page, unsigned long nr_pages);
#define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
#else
#define nth_page(page,n) ((page) + (n))
static inline bool page_range_contiguous(const struct page *page,
unsigned long nr_pages)
{
return true;
}
#endif
/* to align the pointer to the (next) page boundary */

37
mm/cma.c
View File

@ -780,10 +780,8 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
unsigned long count, unsigned int align,
struct page **pagep, gfp_t gfp)
{
unsigned long mask, offset;
unsigned long pfn = -1;
unsigned long start = 0;
unsigned long bitmap_maxno, bitmap_no, bitmap_count;
unsigned long start, pfn, mask, offset;
int ret = -EBUSY;
struct page *page = NULL;
@ -795,7 +793,7 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
if (bitmap_count > bitmap_maxno)
goto out;
for (;;) {
for (start = 0; ; start = bitmap_no + mask + 1) {
spin_lock_irq(&cma->lock);
/*
* If the request is larger than the available number
@ -812,6 +810,22 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
spin_unlock_irq(&cma->lock);
break;
}
pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit);
page = pfn_to_page(pfn);
/*
* Do not hand out page ranges that are not contiguous, so
* callers can just iterate the pages without having to worry
* about these corner cases.
*/
if (!page_range_contiguous(page, count)) {
spin_unlock_irq(&cma->lock);
pr_warn_ratelimited("%s: %s: skipping incompatible area [0x%lx-0x%lx]",
__func__, cma->name, pfn, pfn + count - 1);
continue;
}
bitmap_set(cmr->bitmap, bitmap_no, bitmap_count);
cma->available_count -= count;
/*
@ -821,28 +835,23 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
*/
spin_unlock_irq(&cma->lock);
pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit);
mutex_lock(&cma->alloc_mutex);
ret = alloc_contig_range(pfn, pfn + count, ACR_FLAGS_CMA, gfp);
mutex_unlock(&cma->alloc_mutex);
if (ret == 0) {
page = pfn_to_page(pfn);
if (!ret)
break;
}
cma_clear_bitmap(cma, cmr, pfn, count);
if (ret != -EBUSY)
break;
pr_debug("%s(): memory range at pfn 0x%lx %p is busy, retrying\n",
__func__, pfn, pfn_to_page(pfn));
__func__, pfn, page);
trace_cma_alloc_busy_retry(cma->name, pfn, pfn_to_page(pfn),
count, align);
/* try again with a bit different memory target */
start = bitmap_no + mask + 1;
trace_cma_alloc_busy_retry(cma->name, pfn, page, count, align);
}
out:
if (!ret)
*pagep = page;
return ret;
}
@ -882,7 +891,7 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count,
*/
if (page) {
for (i = 0; i < count; i++)
page_kasan_tag_reset(nth_page(page, i));
page_kasan_tag_reset(page + i);
}
if (ret && !(gfp & __GFP_NOWARN)) {

35
mm/util.c
View File

@ -1281,3 +1281,38 @@ unsigned int folio_pte_batch(struct folio *folio, pte_t *ptep, pte_t pte,
return folio_pte_batch_flags(folio, NULL, ptep, &pte, max_nr, 0);
}
#endif /* CONFIG_MMU */
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
/**
* page_range_contiguous - test whether the page range is contiguous
* @page: the start of the page range.
* @nr_pages: the number of pages in the range.
*
* Test whether the page range is contiguous, such that they can be iterated
* naively, corresponding to iterating a contiguous PFN range.
*
* This function should primarily only be used for debug checks, or when
* working with page ranges that are not naturally contiguous (e.g., pages
* within a folio are).
*
* Returns true if contiguous, otherwise false.
*/
bool page_range_contiguous(const struct page *page, unsigned long nr_pages)
{
const unsigned long start_pfn = page_to_pfn(page);
const unsigned long end_pfn = start_pfn + nr_pages;
unsigned long pfn;
/*
* The memmap is allocated per memory section, so no need to check
* within the first section. However, we need to check each other
* spanned memory section once, making sure the first page in a
* section could similarly be reached by just iterating pages.
*/
for (pfn = ALIGN(start_pfn, PAGES_PER_SECTION);
pfn < end_pfn; pfn += PAGES_PER_SECTION)
if (unlikely(page + (pfn - start_pfn) != pfn_to_page(pfn)))
return false;
return true;
}
#endif