Re: [PATCH v4] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 27 Jan 2025 12:55:11 -0800 (PST) Hugh Dickins <hughd@google.com> wrote:

> > 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@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
> > 
> > ---
> > 
> > v4:
> >   - naming/comments update (by Peter Z.)
> >   - check vma->vma->vm_flags in tlb_free_vma() (by Peter Z.)
> 
> Let me just put on record: you were absolutely right not to extend to
> this the Ack I gave to v3, this v4 is silly (tlb_free_vma() and its
> multiple calls, necessary only because of the unnecessary extra test);
> but I don't see it as doing any actual damage, so I'll stop short of
> NAKking it.

I think I'll just drop this.  Let's revisit in the next -rc cycle,
if Roman is motivated.