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From:   Linus Torvalds <torvalds@linuxfoundation.org>
Date:   Sat, 15 Oct 2022 16:47:16 -0700
Message-ID: <CAHk-=wh+dMSbeuEDatZbtycm9_RFyLe60nigQA8o5w0W_HkQSg@mail.gmail.com>
Subject: Re: [BUG?] X86 arch_tlbbatch_flush() seems to be lacking
 mm_tlb_flush_nested() integration
To:     Nadav Amit <nadav.amit@gmail.com>
Cc:     Jann Horn <jannh@google.com>, Andy Lutomirski <luto@kernel.org>,
        Linux-MM <linux-mm@kvack.org>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>,
        kernel list <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Ingo Molnar <mingo@kernel.org>,
        Sasha Levin <sasha.levin@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
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On Fri, Oct 14, 2022 at 8:51 PM Nadav Amit <nadav.amit@gmail.com> wrote:
>
> Unless I am missing something, flush_tlb_batched_pending() is would be
> called and do the flushing at this point, no?

Ahh, yes.

That seems to be doing the right thing, although looking a bit more at
it, I think it might be improved.

At least in the zap_pte_range() case, instead of doing a synchronous
TLB flush if there are pending batched flushes, it migth be better if
flush_tlb_batched_pending() would set the "need_flush_all" bit in the
mmu_gather structure.

That would possibly avoid that extra TLB flush entirely - since
*normally* fzap_page_range() will cause a TLB flush anyway.

Maybe it doesn't matter.

              Linus