Re: [PATCH v6] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()

[Jann Horn <jannh@google.com>]

On Thu, May 22, 2025 at 3:28 AM Roman Gushchin <roman.gushchin@linux.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@linux.dev>
> Cc: Jann Horn <jannh@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Nick Piggin <npiggin@gmail.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: linux-arch@vger.kernel.org
> Cc: linux-mm@kvack.org

Thanks, this looks better.

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