Message-ID: <20250902051421.162498-1-apopple@nvidia.com>
Date: Tue,  2 Sep 2025 15:14:20 +1000
From: Alistair Popple <apopple@...dia.com>
To: linux-mm@...ck.org,
	akpm@...ux-foundation.org
Cc: david@...hat.com,
	osalvador@...e.de,
	jgg@...pe.ca,
	jhubbard@...dia.com,
	peterx@...hat.com,
	linux-kernel@...r.kernel.org,
	dan.j.williams@...el.com,
	Alistair Popple <apopple@...dia.com>
Subject: [PATCH 1/2] mm/gup: Remove dead pgmap refcounting code

Prior to aed877c2b425 ("device/dax: properly refcount device dax pages
when mapping") ZONE_DEVICE pages were not fully reference counted when
mapped into user page tables. Instead GUP would take a reference on the
associated pgmap to ensure the results of pfn_to_page() remained valid.

This is no longer required and most of the code was removed by
fd2825b0760a ("mm/gup: remove pXX_devmap usage from get_user_pages()").
Finish cleaning this up by removing the dead calls to put_dev_pagemap()
and the temporary context struct.

Signed-off-by: Alistair Popple <apopple@...dia.com>
---
 mm/gup.c | 67 ++++++++++++++++++++++----------------------------------
 1 file changed, 26 insertions(+), 41 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index adffe663594dc..be5791a43c735 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -28,11 +28,6 @@
 #include "internal.h"
 #include "swap.h"
 
-struct follow_page_context {
-	struct dev_pagemap *pgmap;
-	unsigned int page_mask;
-};
-
 static inline void sanity_check_pinned_pages(struct page **pages,
 					     unsigned long npages)
 {
@@ -661,7 +656,7 @@ static inline bool can_follow_write_pud(pud_t pud, struct page *page,
 
 static struct page *follow_huge_pud(struct vm_area_struct *vma,
 				    unsigned long addr, pud_t *pudp,
-				    int flags, struct follow_page_context *ctx)
+				    int flags, unsigned long *page_mask)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct page *page;
@@ -688,7 +683,7 @@ static struct page *follow_huge_pud(struct vm_area_struct *vma,
 	if (ret)
 		page = ERR_PTR(ret);
 	else
-		ctx->page_mask = HPAGE_PUD_NR - 1;
+		*page_mask = HPAGE_PUD_NR - 1;
 
 	return page;
 }
@@ -714,7 +709,7 @@ static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
 static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 				    unsigned long addr, pmd_t *pmd,
 				    unsigned int flags,
-				    struct follow_page_context *ctx)
+				    unsigned long *page_mask)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	pmd_t pmdval = *pmd;
@@ -751,7 +746,7 @@ static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 #endif	/* CONFIG_TRANSPARENT_HUGEPAGE */
 
 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
-	ctx->page_mask = HPAGE_PMD_NR - 1;
+	*page_mask = HPAGE_PMD_NR - 1;
 
 	return page;
 }
@@ -759,7 +754,7 @@ static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 #else  /* CONFIG_PGTABLE_HAS_HUGE_LEAVES */
 static struct page *follow_huge_pud(struct vm_area_struct *vma,
 				    unsigned long addr, pud_t *pudp,
-				    int flags, struct follow_page_context *ctx)
+				    int flags, unsigned long *page_mask)
 {
 	return NULL;
 }
@@ -767,7 +762,7 @@ static struct page *follow_huge_pud(struct vm_area_struct *vma,
 static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 				    unsigned long addr, pmd_t *pmd,
 				    unsigned int flags,
-				    struct follow_page_context *ctx)
+				    unsigned long *page_mask)
 {
 	return NULL;
 }
@@ -813,8 +808,7 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page,
 }
 
 static struct page *follow_page_pte(struct vm_area_struct *vma,
-		unsigned long address, pmd_t *pmd, unsigned int flags,
-		struct dev_pagemap **pgmap)
+		unsigned long address, pmd_t *pmd, unsigned int flags)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct folio *folio;
@@ -912,7 +906,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 				    unsigned long address, pud_t *pudp,
 				    unsigned int flags,
-				    struct follow_page_context *ctx)
+				    unsigned long *page_mask)
 {
 	pmd_t *pmd, pmdval;
 	spinlock_t *ptl;
@@ -926,7 +920,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 	if (!pmd_present(pmdval))
 		return no_page_table(vma, flags, address);
 	if (likely(!pmd_leaf(pmdval)))
-		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+		return follow_page_pte(vma, address, pmd, flags);
 
 	if (pmd_protnone(pmdval) && !gup_can_follow_protnone(vma, flags))
 		return no_page_table(vma, flags, address);
@@ -939,16 +933,16 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 	}
 	if (unlikely(!pmd_leaf(pmdval))) {
 		spin_unlock(ptl);
-		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+		return follow_page_pte(vma, address, pmd, flags);
 	}
 	if (pmd_trans_huge(pmdval) && (flags & FOLL_SPLIT_PMD)) {
 		spin_unlock(ptl);
 		split_huge_pmd(vma, pmd, address);
 		/* If pmd was left empty, stuff a page table in there quickly */
 		return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) :
-			follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+			follow_page_pte(vma, address, pmd, flags);
 	}
-	page = follow_huge_pmd(vma, address, pmd, flags, ctx);
+	page = follow_huge_pmd(vma, address, pmd, flags, page_mask);
 	spin_unlock(ptl);
 	return page;
 }
@@ -956,7 +950,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 static struct page *follow_pud_mask(struct vm_area_struct *vma,
 				    unsigned long address, p4d_t *p4dp,
 				    unsigned int flags,
-				    struct follow_page_context *ctx)
+				    unsigned long *page_mask)
 {
 	pud_t *pudp, pud;
 	spinlock_t *ptl;
@@ -969,7 +963,7 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma,
 		return no_page_table(vma, flags, address);
 	if (pud_leaf(pud)) {
 		ptl = pud_lock(mm, pudp);
-		page = follow_huge_pud(vma, address, pudp, flags, ctx);
+		page = follow_huge_pud(vma, address, pudp, flags, page_mask);
 		spin_unlock(ptl);
 		if (page)
 			return page;
@@ -978,13 +972,13 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma,
 	if (unlikely(pud_bad(pud)))
 		return no_page_table(vma, flags, address);
 
-	return follow_pmd_mask(vma, address, pudp, flags, ctx);
+	return follow_pmd_mask(vma, address, pudp, flags, page_mask);
 }
 
 static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 				    unsigned long address, pgd_t *pgdp,
 				    unsigned int flags,
-				    struct follow_page_context *ctx)
+				    unsigned long *page_mask)
 {
 	p4d_t *p4dp, p4d;
 
@@ -995,7 +989,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 	if (!p4d_present(p4d) || p4d_bad(p4d))
 		return no_page_table(vma, flags, address);
 
-	return follow_pud_mask(vma, address, p4dp, flags, ctx);
+	return follow_pud_mask(vma, address, p4dp, flags, page_mask);
 }
 
 /**
@@ -1003,20 +997,16 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
  * @vma: vm_area_struct mapping @address
  * @address: virtual address to look up
  * @flags: flags modifying lookup behaviour
- * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
- *       pointer to output page_mask
+ * @page_mask: a pointer to output page_mask
  *
  * @flags can have FOLL_ flags set, defined in <linux/mm.h>
  *
- * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
- * the device's dev_pagemap metadata to avoid repeating expensive lookups.
- *
  * When getting an anonymous page and the caller has to trigger unsharing
  * of a shared anonymous page first, -EMLINK is returned. The caller should
  * trigger a fault with FAULT_FLAG_UNSHARE set. Note that unsharing is only
  * relevant with FOLL_PIN and !FOLL_WRITE.
  *
- * On output, the @ctx->page_mask is set according to the size of the page.
+ * On output, @page_mask is set according to the size of the page.
  *
  * Return: the mapped (struct page *), %NULL if no mapping exists, or
  * an error pointer if there is a mapping to something not represented
@@ -1024,7 +1014,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
  */
 static struct page *follow_page_mask(struct vm_area_struct *vma,
 			      unsigned long address, unsigned int flags,
-			      struct follow_page_context *ctx)
+			      unsigned long *page_mask)
 {
 	pgd_t *pgd;
 	struct mm_struct *mm = vma->vm_mm;
@@ -1032,13 +1022,13 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
 
 	vma_pgtable_walk_begin(vma);
 
-	ctx->page_mask = 0;
+	*page_mask = 0;
 	pgd = pgd_offset(mm, address);
 
 	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 		page = no_page_table(vma, flags, address);
 	else
-		page = follow_p4d_mask(vma, address, pgd, flags, ctx);
+		page = follow_p4d_mask(vma, address, pgd, flags, page_mask);
 
 	vma_pgtable_walk_end(vma);
 
@@ -1376,7 +1366,7 @@ static long __get_user_pages(struct mm_struct *mm,
 {
 	long ret = 0, i = 0;
 	struct vm_area_struct *vma = NULL;
-	struct follow_page_context ctx = { NULL };
+	unsigned long page_mask = 0;
 
 	if (!nr_pages)
 		return 0;
@@ -1418,7 +1408,7 @@ static long __get_user_pages(struct mm_struct *mm,
 						pages ? &page : NULL);
 				if (ret)
 					goto out;
-				ctx.page_mask = 0;
+				page_mask = 0;
 				goto next_page;
 			}
 
@@ -1441,7 +1431,7 @@ static long __get_user_pages(struct mm_struct *mm,
 		}
 		cond_resched();
 
-		page = follow_page_mask(vma, start, gup_flags, &ctx);
+		page = follow_page_mask(vma, start, gup_flags, &page_mask);
 		if (!page || PTR_ERR(page) == -EMLINK) {
 			ret = faultin_page(vma, start, gup_flags,
 					   PTR_ERR(page) == -EMLINK, locked);
@@ -1474,7 +1464,7 @@ static long __get_user_pages(struct mm_struct *mm,
 			goto out;
 		}
 next_page:
-		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
+		page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
 		if (page_increm > nr_pages)
 			page_increm = nr_pages;
 
@@ -1524,8 +1514,6 @@ static long __get_user_pages(struct mm_struct *mm,
 		nr_pages -= page_increm;
 	} while (nr_pages);
 out:
-	if (ctx.pgmap)
-		put_dev_pagemap(ctx.pgmap);
 	return i ? i : ret;
 }
 
@@ -2853,7 +2841,6 @@ 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)
 {
-	struct dev_pagemap *pgmap = NULL;
 	int ret = 0;
 	pte_t *ptep, *ptem;
 
@@ -2926,8 +2913,6 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
 	ret = 1;
 
 pte_unmap:
-	if (pgmap)
-		put_dev_pagemap(pgmap);
 	pte_unmap(ptem);
 	return ret;
 }
-- 
2.47.2

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