From d6d6d21dbf435d8030782a627175e36e6c7b2dfb Mon Sep 17 00:00:00 2001
From: David Hildenbrand <redacted>
Date: Sat, 6 Sep 2025 08:33:42 +0200
Subject: [PATCH] tmp

Signed-off-by: David Hildenbrand <redacted>
---
 mm/gup.c | 79 ++++++++++++++++++++++++++------------------------------
 1 file changed, 36 insertions(+), 43 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 22420f2069ee1..98907ead749c0 100644
--- a/mm/gup.c
+++ b/mm/gup.c

@@ -2845,12 +2845,11 @@ static void __maybe_unused gup_fast_undo_dev_pagemap(int *nr, int nr_start,
  * also check pmd here to make sure pmd doesn't change (corresponds to
  * pmdp_collapse_flush() in the THP collapse code path).
  */
-static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
+		unsigned long end, unsigned int flags, struct page **pages)
 {
 	struct dev_pagemap *pgmap = NULL;
-	int ret = 0;
+	unsigned long nr_pages = 0;
 	pte_t *ptep, *ptem;
 	ptem = ptep = pte_offset_map(&pmd, addr);

@@ -2908,24 +2907,20 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
 		 * details.
 		 */
 		if (flags & FOLL_PIN) {
-			ret = arch_make_folio_accessible(folio);
-			if (ret) {
+			if (arch_make_folio_accessible(folio)) {
 				gup_put_folio(folio, 1, flags);
 				goto pte_unmap;
 			}
 		}
 		folio_set_referenced(folio);
-		pages[*nr] = page;
-		(*nr)++;
+		pages[nr_pages++] = page;
 	} while (ptep++, addr += PAGE_SIZE, addr != end);
-	ret = 1;
-
 pte_unmap:
 	if (pgmap)
 		put_dev_pagemap(pgmap);
 	pte_unmap(ptem);
-	return ret;
+	return nr_pages;
 }
 #else

@@ -2938,21 +2933,24 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
  * get_user_pages_fast_only implementation that can pin pages. Thus it's still
  * useful to have gup_fast_pmd_leaf even if we can't operate on ptes.
  */
-static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
+		unsigned long end, unsigned int flags, struct page **pages)
 {
 	return 0;
 }
 #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
-static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
+		unsigned long end, unsigned int flags, struct page **pages)
 {
+	const unsigned long nr_pages = (end - addr) >> PAGE_SHIFT;
 	struct page *page;
 	struct folio *folio;
-	int refs;
+	unsigned long i;
+
+	/* See gup_fast_pte_range() */
+	if (pmd_protnone(orig))
+		return 0;
 	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
 		return 0;

@@ -2960,33 +2958,30 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (pmd_special(orig))
 		return 0;
-	refs = (end - addr) >> PAGE_SHIFT;
 	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
-	folio = try_grab_folio_fast(page, refs, flags);
+	folio = try_grab_folio_fast(page, nr_pages, flags);
 	if (!folio)
 		return 0;
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
-		gup_put_folio(folio, refs, flags);
+		gup_put_folio(folio, nr_pages, flags);
 		return 0;
 	}
 	if (!gup_fast_folio_allowed(folio, flags)) {
-		gup_put_folio(folio, refs, flags);
+		gup_put_folio(folio, nr_pages, flags);
 		return 0;
 	}
 	if (!pmd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
-		gup_put_folio(folio, refs, flags);
+		gup_put_folio(folio, nr_pages, flags);
 		return 0;
 	}
-	pages += *nr;
-	*nr += refs;
-	for (; refs; refs--)
+	for (i = 0; i < nr_pages; i++)
 		*(pages++) = page++;
 	folio_set_referenced(folio);
-	return 1;
+	return nr_pages;
 }
 static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,

@@ -3033,11 +3028,11 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
 	return 1;
 }
-static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
+		unsigned long end, unsigned int flags, struct page **pages)
 {
-	unsigned long next;
+	unsigned long cur_nr_pages, next;
+	unsigned long nr_pages = 0;
 	pmd_t *pmdp;
 	pmdp = pmd_offset_lockless(pudp, pud, addr);

@@ -3046,23 +3041,21 @@ static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
 		next = pmd_addr_end(addr, end);
 		if (!pmd_present(pmd))
-			return 0;
+			break;
-		if (unlikely(pmd_leaf(pmd))) {
-			/* See gup_fast_pte_range() */
-			if (pmd_protnone(pmd))
-				return 0;
+		if (unlikely(pmd_leaf(pmd)))
+			cur_nr_pages = gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags, pages);
+		else
+			cur_nr_pages = gup_fast_pte_range(pmd, pmdp, addr, next, flags, pages);
-			if (!gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags,
-				pages, nr))
-				return 0;
+		nr_pages += cur_nr_pages;
+		pages += cur_nr_pages;
-		} else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags,
-					       pages, nr))
-			return 0;
+		if (nr_pages != (next - addr) >> PAGE_SIZE)
+			break;
 	} while (pmdp++, addr = next, addr != end);
-	return 1;
+	return nr_pages;
 }
 static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,

--
2.50.1



Oh, I might even have found a bug moving away from that questionable
"ret==1 means success" handling in gup_fast_pte_range()? Will
have to double-check, but likely the following is the right thing to do.



From 8f48b25ef93e7ef98611fd58ec89384ad5171782 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <redacted>
Date: Sat, 6 Sep 2025 08:46:45 +0200
Subject: [PATCH] mm/gup: fix handling of errors from
 arch_make_folio_accessible() in follow_page_pte()

In case we call arch_make_folio_accessible() and it fails, we would
incorrectly return a value that is "!= 0" to the caller, indicating that
we pinned all requested pages and that the caller can keep going.

follow_page_pte() is not supposed to return error values, but instead
0 on failure and 1 on success.

That is of course wrong, because the caller will just keep going pinning
more pages. If we happen to pin a page afterwards, we're in trouble,
because we essentially skipped some pages.

Fixes: f28d43636d6f ("mm/gup/writeback: add callbacks for inaccessible pages")
Signed-off-by: David Hildenbrand <redacted>
---
 mm/gup.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 22420f2069ee1..cff226ec0ee7d 100644
--- a/mm/gup.c
+++ b/mm/gup.c

@@ -2908,8 +2908,7 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
 		 * details.
 		 */
 		if (flags & FOLL_PIN) {
-			ret = arch_make_folio_accessible(folio);
-			if (ret) {
+			if (arch_make_folio_accessible(folio)) {