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Message-ID: <20250507154105.763088-2-p.antoniou@partner.samsung.com>
Date: Wed, 7 May 2025 10:41:05 -0500
From: Pantelis Antoniou <p.antoniou@...tner.samsung.com>
To: Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>
CC: <linux-kernel@...r.kernel.org>, Artem Krupotkin <artem.k@...sung.com>,
Charles Briere <c.briere@...sung.com>, Wade Farnsworth
<wade.farnsworth@...mens.com>
Subject: [PATCH 1/1] Fix zero copy I/O on __get_user_pages allocated pages
Recent updates to net filesystems enabled zero copy operations,
which require getting a user space page pinned.
This does not work for pages that were allocated via __get_user_pages
and then mapped to user-space via remap_pfn_rage.
remap_pfn_range_internal() will turn on VM_IO | VM_PFNMAP vma bits.
VM_PFNMAP in particular mark the pages as not having struct_page
associated with them, which is not the case for __get_user_pages()
This in turn makes any attempt to lock a page fail, and breaking
I/O from that address range.
This patch address it by special casing pages in those VMAs and not
calling vm_normal_page() for them.
Signed-off-by: Pantelis Antoniou <p.antoniou@...tner.samsung.com>
---
mm/gup.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 84461d384ae2..e185c18c0c81 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -833,6 +833,20 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page,
return !userfaultfd_pte_wp(vma, pte);
}
+static struct page *gup_normal_page(struct vm_area_struct *vma,
+ unsigned long address, pte_t pte)
+{
+ unsigned long pfn;
+
+ if (vma->vm_flags & (VM_MIXEDMAP | VM_PFNMAP)) {
+ pfn = pte_pfn(pte);
+ if (!pfn_valid(pfn) || is_zero_pfn(pfn) || pfn > highest_memmap_pfn)
+ return NULL;
+ return pfn_to_page(pfn);
+ }
+ return vm_normal_page(vma, address, pte);
+}
+
static struct page *follow_page_pte(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd, unsigned int flags,
struct dev_pagemap **pgmap)
@@ -858,7 +872,9 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
if (pte_protnone(pte) && !gup_can_follow_protnone(vma, flags))
goto no_page;
- page = vm_normal_page(vma, address, pte);
+ page = gup_normal_page(vma, address, pte);
+ if (page && (vma->vm_flags & (VM_MIXEDMAP | VM_PFNMAP)))
+ (void)follow_pfn_pte(vma, address, ptep, flags);
/*
* We only care about anon pages in can_follow_write_pte() and don't
@@ -1130,7 +1146,7 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
*vma = get_gate_vma(mm);
if (!page)
goto out;
- *page = vm_normal_page(*vma, address, entry);
+ *page = gup_normal_page(*vma, address, entry);
if (!*page) {
if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(entry)))
goto unmap;
@@ -1271,8 +1287,6 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
int foreign = (gup_flags & FOLL_REMOTE);
bool vma_anon = vma_is_anonymous(vma);
- if (vm_flags & (VM_IO | VM_PFNMAP))
- return -EFAULT;
if ((gup_flags & FOLL_ANON) && !vma_anon)
return -EFAULT;
--
2.25.1
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