Message-ID: <508B59B0.5010503@redhat.com>
Date: Fri, 26 Oct 2012 23:49:04 -0400
From: Rik van Riel <riel@redhat.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: Ingo Molnar <mingo@kernel.org>, Andi Kleen <andi@firstfloor.org>,
        Michel Lespinasse <walken@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrea Arcangeli <aarcange@redhat.com>, Mel Gorman <mgorman@suse.de>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/3] x86,mm: drop TLB flush from ptep_set_access_flags
References: <20121025121617.617683848@chello.nl> <20121025124832.840241082@chello.nl> <CA+55aFxRh43832cEW39t0+d1Sdz46Up6Za9w641jpWukmi4zFw@mail.gmail.com> <5089F5B5.1050206@redhat.com> <CA+55aFwcj=nh1RUmEXUk6W3XwfbdQdQofkkCstbLGVo1EoKryA@mail.gmail.com> <508A0A0D.4090001@redhat.com> <CA+55aFx2fSdDcFxYmu00JP9rHiZ1BjH3tO4CfYXOhf_rjRP_Eg@mail.gmail.com> <CANN689EHj2inp+wjJGcqMHZQUV3Xm+3dAkLPOsnV4RZU+Kq5nA@mail.gmail.com> <m2pq45qu0s.fsf@firstfloor.org> <508A8D31.9000106@redhat.com> <20121026132601.GC9886@gmail.com> <20121026144502.6e94643e@dull> <20121026221254.7d32c8bf@pyramind.ukuu.org.uk>
In-Reply-To: <20121026221254.7d32c8bf@pyramind.ukuu.org.uk>
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On 10/26/2012 05:12 PM, Alan Cox wrote:
> On Fri, 26 Oct 2012 14:45:02 -0400
> Rik van Riel <riel@redhat.com> wrote:
>
>> Intel has an architectural guarantee that the TLB entry causing
>> a page fault gets invalidated automatically. This means
>> we should be able to drop the local TLB invalidation.
>>
>> Because of the way other areas of the page fault code work,
>> chances are good that all x86 CPUs do this.  However, if
>> someone somewhere has an x86 CPU that does not invalidate
>> the TLB entry causing a page fault, this one-liner should
>> be easy to revert.
>
> This does not strike me as a good standard of validation for such a change
>
> At the very least we should have an ACK from AMD and from VIA, and
> preferably ping RDC and some of the other embedded folks. Given an AMD
> and VIA ACK I'd be fine. I doubt anyone knows any more what Cyrix CPUs
> did or cared about and I imagine H Peter or Linus can answer for
> Transmeta ;-)

Fair enough.

If it turns out any of those CPUs need an explicit
flush, then we can also adjust flush_tlb_fix_spurious_fault
to actually do a local flush on x86 (or at least on those
CPUs).

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