mm: gup: cleanup the gup_fast_*() call chain

Refactor gup_fast functions so each step of the way returns the number of
pages pinned. Because the previous step of the chain knows what the number
it should be, less indicates an error. This way there's no need to pass *nr
along.

Suggested-by: David Hildenbrand <david@kernel.org>
Link: https://lore.kernel.org/all/85e760cf-b994-40db-8d13-221feee55c60@redhat.com/T/#u
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Aristeu Rozanski <aris@ruivo.org>
Link: https://patch.msgid.link/20260828015542.334186653@ruivo.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

1 files changed, 94 insertions, 85 deletions

diff --git a/mm/gup.c b/mm/gup.c
index bd981ab39751..a4036c02e213 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2826,11 +2826,11 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
  * 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)
 {
-	int ret = 0;
+	unsigned long nr_pages = 0;
 	pte_t *ptep, *ptem;
 
 	ptem = ptep = pte_offset_map(&pmd, addr);
@@ -2892,15 +2892,13 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
 			goto pte_unmap;
 		}
 		folio_set_referenced(folio);
-		pages[*nr] = page;
-		(*nr)++;
+		pages[nr_pages] = page;
+		nr_pages++;
 	} while (ptep++, addr += PAGE_SIZE, addr != end);
 
-	ret = 1;
-
 pte_unmap:
 	pte_unmap(ptem);
-	return ret;
+	return nr_pages;
 }
 #else
 
@@ -2913,21 +2911,21 @@ pte_unmap:
  * 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)
 {
 	struct page *page;
 	struct folio *folio;
-	int refs;
+	unsigned long nr_pages, i;
 
 	/* See gup_fast_pte_range() */
 	if (pmd_protnone(orig))
@@ -2939,42 +2937,40 @@ 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;
+	nr_pages = (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_get_lockless(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,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pud_leaf(pud_t orig, pud_t *pudp,
+		unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages)
 {
 	struct page *page;
 	struct folio *folio;
-	int refs;
+	unsigned long nr_pages, i;
 
 	if (!pud_access_permitted(orig, flags & FOLL_WRITE))
 		return 0;
@@ -2982,41 +2978,39 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
 	if (pud_special(orig))
 		return 0;
 
-	refs = (end - addr) >> PAGE_SHIFT;
+	nr_pages = (end - addr) >> PAGE_SHIFT;
 	page = pud_page(orig) + ((addr & ~PUD_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(pud_val(orig) != pud_val(pudp_get(pudp)))) {
-		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 (!pud_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_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 next, nr_pages = 0, chunk_nr_pages;
 	pmd_t *pmdp;
 
 	pmdp = pmd_offset_lockless(pudp, pud, addr);
@@ -3025,26 +3019,30 @@ 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))) {
-			if (!gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags,
-				pages, nr))
-				return 0;
-
-		} else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags,
-					       pages, nr))
-			return 0;
+			chunk_nr_pages = gup_fast_pmd_leaf(pmd, pmdp, addr,
+							   next, flags,
+							   &pages[nr_pages]);
+
+		} else
+			chunk_nr_pages = gup_fast_pte_range(pmd, pmdp, addr,
+							    next, flags,
+							    &pages[nr_pages]);
+		nr_pages += chunk_nr_pages;
+		if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+			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,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d,
+		unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages)
 {
-	unsigned long next;
+	unsigned long next, nr_pages = 0, chunk_nr_pages;
 	pud_t *pudp;
 
 	pudp = pud_offset_lockless(p4dp, p4d, addr);
@@ -3053,24 +3051,27 @@ static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,
 
 		next = pud_addr_end(addr, end);
 		if (unlikely(!pud_present(pud)))
-			return 0;
-		if (unlikely(pud_leaf(pud))) {
-			if (!gup_fast_pud_leaf(pud, pudp, addr, next, flags,
-					       pages, nr))
-				return 0;
-		} else if (!gup_fast_pmd_range(pudp, pud, addr, next, flags,
-					       pages, nr))
-			return 0;
+			break;
+		if (unlikely(pud_leaf(pud)))
+			chunk_nr_pages = gup_fast_pud_leaf(pud, pudp, addr,
+							   next, flags,
+							   &pages[nr_pages]);
+		else
+			chunk_nr_pages = gup_fast_pmd_range(pudp, pud, addr,
+							    next, flags,
+							    &pages[nr_pages]);
+		nr_pages += chunk_nr_pages;
+		if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+			break;
 	} while (pudp++, addr = next, addr != end);
 
-	return 1;
+	return nr_pages;
 }
 
-static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages,
-		int *nr)
+static unsigned long gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
+		unsigned long end, unsigned int flags, struct page **pages)
 {
-	unsigned long next;
+	unsigned long next, nr_pages = 0, chunk_nr_pages;
 	p4d_t *p4dp;
 
 	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
@@ -3079,20 +3080,23 @@ static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 
 		next = p4d_addr_end(addr, end);
 		if (!p4d_present(p4d))
-			return 0;
+			break;
 		BUILD_BUG_ON(p4d_leaf(p4d));
-		if (!gup_fast_pud_range(p4dp, p4d, addr, next, flags,
-					pages, nr))
-			return 0;
+		chunk_nr_pages = gup_fast_pud_range(p4dp, p4d, addr, next,
+						    flags, &pages[nr_pages]);
+		nr_pages += chunk_nr_pages;
+		if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+			break;
 	} while (p4dp++, addr = next, addr != end);
 
-	return 1;
+	return nr_pages;
 }
 
-static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
-		unsigned int flags, struct page **pages, int *nr)
+static unsigned long gup_fast_pgd_range(unsigned long addr,
+		unsigned long end, unsigned int flags,
+		struct page **pages)
 {
-	unsigned long next;
+	unsigned long next, nr_pages = 0, chunk_nr_pages;
 	pgd_t *pgdp;
 
 	pgdp = pgd_offset(current->mm, addr);
@@ -3101,17 +3105,23 @@ static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
 
 		next = pgd_addr_end(addr, end);
 		if (pgd_none(pgd))
-			return;
+			break;
 		BUILD_BUG_ON(pgd_leaf(pgd));
-		if (!gup_fast_p4d_range(pgdp, pgd, addr, next, flags,
-					pages, nr))
-			return;
+		chunk_nr_pages = gup_fast_p4d_range(pgdp, pgd, addr, next,
+						    flags, &pages[nr_pages]);
+		nr_pages += chunk_nr_pages;
+		if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+			break;
 	} while (pgdp++, addr = next, addr != end);
+
+	return nr_pages;
 }
 #else
-static inline void gup_fast_pgd_range(unsigned long addr, unsigned long end,
-		unsigned int flags, struct page **pages, int *nr)
+static inline unsigned long gup_fast_pgd_range(unsigned long addr,
+		unsigned long end, unsigned int flags,
+		struct page **pages)
 {
+	return 0;
 }
 #endif /* CONFIG_HAVE_GUP_FAST */
 
@@ -3129,8 +3139,7 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
 static unsigned long gup_fast(unsigned long start, unsigned long end,
 		unsigned int gup_flags, struct page **pages)
 {
-	unsigned long flags;
-	int nr_pinned = 0;
+	unsigned long flags, nr_pinned;
 	unsigned seq;
 
 	if (!IS_ENABLED(CONFIG_HAVE_GUP_FAST) ||
@@ -3154,7 +3163,7 @@ static unsigned long gup_fast(unsigned long start, unsigned long end,
 	 * that come from callers of tlb_remove_table_sync_one().
 	 */
 	local_irq_save(flags);
-	gup_fast_pgd_range(start, end, gup_flags, pages, &nr_pinned);
+	nr_pinned = gup_fast_pgd_range(start, end, gup_flags, pages);
 	local_irq_restore(flags);
 
 	/*