[PATCH v3 3/4] selftests/mm: reimplement is_backed_by_thp() with more precise check

[Zi Yan <ziy@nvidia.com>]

and rename it to is_backed_by_folio().

is_backed_by_folio() checks if the given vaddr is backed a folio with
a given order. It does so by:
1. getting the pfn of the vaddr;
2. checking kpageflags of the pfn;

if order is greater than 0:
3. checking kpageflags of the head pfn;
4. checking kpageflags of all tail pfns.

pmd_order is added to split_huge_page_test.c and replaces max_order.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 .../selftests/mm/split_huge_page_test.c       | 67 +++++++++++++------
 tools/testing/selftests/mm/vm_util.c          |  2 +-
 tools/testing/selftests/mm/vm_util.h          |  1 +
 3 files changed, 48 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 63ac82f0b9e0..3aaf783f339f 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -25,6 +25,7 @@
 uint64_t pagesize;
 unsigned int pageshift;
 uint64_t pmd_pagesize;
+unsigned int pmd_order;
 
 #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
 #define SMAP_PATH "/proc/self/smaps"
@@ -36,23 +37,48 @@ uint64_t pmd_pagesize;
 
 #define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
 
-int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
+int is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd)
 {
-	uint64_t paddr;
-	uint64_t page_flags;
+	unsigned long pfn_head;
+	uint64_t pfn_flags;
+	unsigned long pfn;
+	unsigned long i;
 
-	if (pagemap_file) {
-		pread(pagemap_file, &paddr, sizeof(paddr),
-			((long)vaddr >> pageshift) * sizeof(paddr));
+	if (!pagemap_fd || !kpageflags_fd)
+		return 0;
 
-		if (kpageflags_file) {
-			pread(kpageflags_file, &page_flags, sizeof(page_flags),
-				PAGEMAP_PFN(paddr) * sizeof(page_flags));
+	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
 
-			return !!(page_flags & KPF_THP);
-		}
+	if (pfn == -1UL)
+		return 0;
+
+	if (get_pfn_flags(pfn, kpageflags_fd, &pfn_flags))
+		return 0;
+
+	if (!order) {
+		if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))
+			return 0;
+		return 1;
 	}
-	return 0;
+
+	if (!(pfn_flags & KPF_THP))
+		return 0;
+
+	pfn_head = pfn & ~((1 << order) - 1);
+
+	if (get_pfn_flags(pfn_head, kpageflags_fd, &pfn_flags))
+		return 0;
+
+	if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD)))
+		return 0;
+
+	for (i = 1; i < (1UL << order) - 1; i++) {
+		if (get_pfn_flags(pfn_head + i, kpageflags_fd, &pfn_flags))
+			return 0;
+		if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)))
+			return 0;
+	}
+	return 1;
 }
 
 static void write_file(const char *path, const char *buf, size_t buflen)
@@ -233,7 +259,7 @@ void split_pte_mapped_thp(void)
 	thp_size = 0;
 	for (i = 0; i < pagesize * 4; i++)
 		if (i % pagesize == 0 &&
-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
+		    is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
 			thp_size++;
 
 	if (thp_size != 4)
@@ -250,7 +276,7 @@ void split_pte_mapped_thp(void)
 			ksft_exit_fail_msg("%ld byte corrupted\n", i);
 
 		if (i % pagesize == 0 &&
-		    is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
+		    !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, kpageflags_fd))
 			thp_size++;
 	}
 
@@ -522,7 +548,6 @@ int main(int argc, char **argv)
 	const char *fs_loc;
 	bool created_tmp;
 	int offset;
-	unsigned int max_order;
 	unsigned int nr_pages;
 	unsigned int tests;
 
@@ -543,28 +568,28 @@ int main(int argc, char **argv)
 		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
 
 	nr_pages = pmd_pagesize / pagesize;
-	max_order = GET_ORDER(nr_pages);
-	tests = 2 + (max_order - 1) + (2 * max_order) + (max_order - 1) * 4 + 2;
+	pmd_order = GET_ORDER(nr_pages);
+	tests = 2 + (pmd_order - 1) + (2 * pmd_order) + (pmd_order - 1) * 4 + 2;
 	ksft_set_plan(tests);
 
 	fd_size = 2 * pmd_pagesize;
 
 	split_pmd_zero_pages();
 
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		if (i != 1)
 			split_pmd_thp_to_order(i);
 
 	split_pte_mapped_thp();
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		split_file_backed_thp(i);
 
 	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
 			&fs_loc);
-	for (i = max_order - 1; i >= 0; i--)
+	for (i = pmd_order - 1; i >= 0; i--)
 		split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, -1);
 
-	for (i = 0; i < max_order; i++)
+	for (i = 0; i < pmd_order; i++)
 		for (offset = 0;
 		     offset < nr_pages;
 		     offset += MAX(nr_pages / 4, 1 << i))
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 4d952d1bc96d..193ba1a1a3cc 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -338,7 +338,7 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
 	return count;
 }
 
-static int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
+int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
 {
 	size_t count;
 
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 02e3f1e7065b..148b792cff0f 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -92,6 +92,7 @@ unsigned long default_huge_page_size(void);
 int detect_hugetlb_page_sizes(size_t sizes[], int max);
 int check_folio_orders(char *vaddr_start, size_t len, int pagemap_file,
 			int kpageflags_file, int orders[], int nr_orders);
+int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.47.2