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.
Reviewed-by: Alexandru Elisei alexandru.elisei@arm.com Signed-off-by: David Hildenbrand david@redhat.com --- include/linux/mm.h | 6 ++++++ mm/cma.c | 39 ++++++++++++++++++++++++--------------- mm/util.c | 33 +++++++++++++++++++++++++++++++++ 3 files changed, 63 insertions(+), 15 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index f6880e3225c5c..2ca1eb2db63ec 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -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 */ diff --git a/mm/cma.c b/mm/cma.c index e56ec64d0567e..813e6dc7b0954 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -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; /* @@ -821,29 +835,24 @@ 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: - *pagep = page; + 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)) { diff --git a/mm/util.c b/mm/util.c index d235b74f7aff7..0bf349b19b652 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1280,4 +1280,37 @@ 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); } + +#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. We need to check + * each involved memory section once. + */ + 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 #endif /* CONFIG_MMU */