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Message-ID: <20250127195321.35779-1-roman.gushchin@linux.dev>
Date: Mon, 27 Jan 2025 19:53:21 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Jann Horn <jannh@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
Nick Piggin <npiggin@...il.com>,
Hugh Dickins <hughd@...gle.com>,
linux-arch@...r.kernel.org
Subject: [PATCH v4] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()
Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas")
added a forced tlbflush to tlb_vma_end(), which is required to avoid a
race between munmap() and unmap_mapping_range(). However it added some
overhead to other paths where tlb_vma_end() is used, but vmas are not
removed, e.g. madvise(MADV_DONTNEED).
Fix this by moving the tlb flush out of tlb_end_vma() into
free_pgtables(), somewhat similar to the stable version of the
original commit: e.g. stable commit 895428ee124a ("mm: Force TLB flush
for PFNMAP mappings before unlink_file_vma()").
Note, that if tlb->fullmm is set, no flush is required, as the whole
mm is about to be destroyed.
Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Jann Horn <jannh@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Nick Piggin <npiggin@...il.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: linux-arch@...r.kernel.org
Cc: linux-mm@...ck.org
---
v4:
- naming/comments update (by Peter Z.)
- check vma->vma->vm_flags in tlb_free_vma() (by Peter Z.)
v3:
- added initialization of vma_pfn in __tlb_reset_range() (by Hugh D.)
v2:
- moved vma_pfn flag handling into tlb.h (by Peter Z.)
- added comments (by Peter Z.)
- fixed the vma_pfn flag setting (by Hugh D.)
---
include/asm-generic/tlb.h | 49 +++++++++++++++++++++++++++++++--------
mm/memory.c | 2 ++
2 files changed, 41 insertions(+), 10 deletions(-)
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index e402aef79c93..dd673ec59893 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -58,6 +58,11 @@
* Defaults to flushing at tlb_end_vma() to reset the range; helps when
* there's large holes between the VMAs.
*
+ * - tlb_free_vma()
+ *
+ * tlb_free_vma() marks the start of unlinking the vma and freeing
+ * page-tables.
+ *
* - tlb_remove_table()
*
* tlb_remove_table() is the basic primitive to free page-table directories
@@ -400,7 +405,10 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb)
* Do not reset mmu_gather::vma_* fields here, we do not
* call into tlb_start_vma() again to set them if there is an
* intermediate flush.
+ *
+ * Except for vma_pfn, that only cares if there's pending TLBI.
*/
+ tlb->vma_pfn = 0;
}
#ifdef CONFIG_MMU_GATHER_NO_RANGE
@@ -465,7 +473,12 @@ tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma)
*/
tlb->vma_huge = is_vm_hugetlb_page(vma);
tlb->vma_exec = !!(vma->vm_flags & VM_EXEC);
- tlb->vma_pfn = !!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP));
+
+ /*
+ * Track if there's at least one VM_PFNMAP/VM_MIXEDMAP vma
+ * in the tracked range, see tlb_free_vma().
+ */
+ tlb->vma_pfn |= !!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP));
}
static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
@@ -564,23 +577,39 @@ static inline void tlb_start_vma(struct mmu_gather *tlb, struct vm_area_struct *
}
static inline void tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
+{
+ if (tlb->fullmm || IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS))
+ return;
+
+ /*
+ * Do a TLB flush and reset the range at VMA boundaries; this avoids
+ * the ranges growing with the unused space between consecutive VMAs,
+ * but also the mmu_gather::vma_* flags from tlb_start_vma() rely on
+ * this.
+ */
+ tlb_flush_mmu_tlbonly(tlb);
+}
+
+static inline void tlb_free_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
if (tlb->fullmm)
return;
/*
* VM_PFNMAP is more fragile because the core mm will not track the
- * page mapcount -- there might not be page-frames for these PFNs after
- * all. Force flush TLBs for such ranges to avoid munmap() vs
- * unmap_mapping_range() races.
+ * page mapcount -- there might not be page-frames for these PFNs
+ * after all.
+ *
+ * Specifically() there is a race between munmap() and
+ * unmap_mapping_range(), where munmap() will unlink the VMA, such
+ * that unmap_mapping_range() will no longer observe the VMA and
+ * no-op, without observing the TLBI, returning prematurely.
+ *
+ * So if we're about to unlink such a VMA, and we have pending
+ * TLBI for such a vma, flush things now.
*/
- if (tlb->vma_pfn || !IS_ENABLED(CONFIG_MMU_GATHER_MERGE_VMAS)) {
- /*
- * Do a TLB flush and reset the range at VMA boundaries; this avoids
- * the ranges growing with the unused space between consecutive VMAs.
- */
+ if ((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) && tlb->vma_pfn)
tlb_flush_mmu_tlbonly(tlb);
- }
}
/*
diff --git a/mm/memory.c b/mm/memory.c
index 539c0f7c6d54..4ea5e286c68f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -378,6 +378,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
if (unlikely(xa_is_zero(next)))
next = NULL;
+ tlb_free_vma(tlb, vma);
/*
* Hide vma from rmap and truncate_pagecache before freeing
* pgtables
@@ -403,6 +404,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
next = mas_find(mas, ceiling - 1);
if (unlikely(xa_is_zero(next)))
next = NULL;
+ tlb_free_vma(tlb, vma);
if (mm_wr_locked)
vma_start_write(vma);
unlink_anon_vmas(vma);
--
2.48.1.262.g85cc9f2d1e-goog
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