From: "Kiryl Shutsemau (Meta)" <[email protected]> is_backed_by_folio() answers "what order folio backs this page", but mTHP collapse tests need the range-level question: is every order-aligned window of this VA range backed by one folio of exactly that order, mapped head-to-tail?
Add is_range_backed_by_folio_orders(): per window, require a present and naturally aligned head PFN, a contiguous PFN run across the window, and is_backed_by_folio() agreeing on the order. A window assembled from pieces of different folios, or mapping a folio outside its natural position, fails the check. Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]> --- tools/testing/selftests/mm/vm_util.c | 46 ++++++++++++++++++++++++++++ tools/testing/selftests/mm/vm_util.h | 2 ++ 2 files changed, 48 insertions(+) diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c index 343a15e25a9f..793342095420 100644 --- a/tools/testing/selftests/mm/vm_util.c +++ b/tools/testing/selftests/mm/vm_util.c @@ -365,6 +365,52 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, return false; } +/* + * Check whether the range [start, start + len) is backed by folios of + * exactly @order, mapped at their natural alignment. + * + * is_backed_by_folio() classifies the folio backing one page; here we + * additionally require that each order-aligned window of the range maps + * one such folio head-to-tail: the VA range must be naturally aligned, + * each window's PFN run must be contiguous, and the first PFN must be + * the (naturally aligned) folio head. + * + * This is the check "did this range collapse into order-@order folios": + * a window assembled from parts of several folios, or mapping a folio + * shifted from its natural position, fails. + */ +bool is_range_backed_by_folio_orders(char *start, size_t len, int order, + int pagemap_fd, int kpageflags_fd) +{ + const unsigned long nr_pages = 1UL << order; + const size_t window = nr_pages * psize(); + char *vaddr; + + if ((uintptr_t)start % window || len % window) + return false; + + for (vaddr = start; vaddr < start + len; vaddr += window) { + unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr); + unsigned long i; + + /* Not present, or not mapping the folio head. */ + if (pfn == -1UL || pfn % nr_pages) + return false; + + for (i = 1; i < nr_pages; i++) { + if (pagemap_get_pfn(pagemap_fd, vaddr + i * psize()) != + pfn + i) + return false; + } + + if (!is_backed_by_folio(vaddr, order, pagemap_fd, + kpageflags_fd)) + return false; + } + + return true; +} + /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */ int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len, bool miss, bool wp, bool minor, uint64_t *ioctls) diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h index 5eb90e0d1d13..76e9938a908e 100644 --- a/tools/testing/selftests/mm/vm_util.h +++ b/tools/testing/selftests/mm/vm_util.h @@ -97,6 +97,8 @@ int64_t allocate_transhuge(void *ptr, int pagemap_fd); int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags); bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd); +bool is_range_backed_by_folio_orders(char *start, size_t len, int order, + int pagemap_fd, int kpageflags_fd); int uffd_register(int uffd, void *addr, uint64_t len, bool miss, bool wp, bool minor); -- 2.54.0
