linux-kernel - Re: [PATCH v6] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free

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Message-ID: <CAG48ez303kEZ8rWrP9AvsWGddcptAxuk6C56eBQ1Z6RJW-a_mw@mail.gmail.com>
Date: Thu, 22 May 2025 20:00:54 +0200
From: Jann Horn <jannh@...gle.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-arch@...r.kernel.org, 
	Will Deacon <will@...nel.org>, "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>, 
	Nick Piggin <npiggin@...il.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v6] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP
 vmas into free_pgtables()

On Thu, May 22, 2025 at 3:28 AM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> 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 new
> tlb_flush_vmas() called from free_pgtables(), somewhat similar to the
> stable version of the original commit:
> 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

Thanks, this looks better.

Reviewed-by: Jann Horn <jannh@...gle.com>