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From: Shentino <shentino@gmail.com>
Date: Sat, 17 Nov 2012 13:53:26 -0800
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Subject: Re: [PATCH 2/3] x86,mm: drop TLB flush from ptep_set_access_flags
To: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Ingo Molnar <mingo@kernel.org>, Andi Kleen <andi@firstfloor.org>,
        Michel Lespinasse <walken@google.com>,
        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 Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, Florian Fainelli <florian@openwrt.org>,
        Borislav Petkov <borislav.petkov@amd.com>
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On Sat, Nov 17, 2012 at 7:24 AM, Rik van Riel <riel@redhat.com> wrote:
> On 11/17/2012 09:56 AM, Linus Torvalds wrote:
>>
>> On Sat, Nov 17, 2012 at 6:50 AM, Borislav Petkov <bp@alien8.de> wrote:
>>>
>>> I don't know, however, whether it would be prudent to have some sort of
>>> a cheap assertion in the code (cheaper than INVLPG %ADDR, although on
>>> older cpus we do MOV CR3) just in case. This should be enabled only with
>>> DEBUG_VM on, of course...
>>
>>
>> I wonder how we could actually test for it. We'd have to have some
>> per-cpu page-fault address check (along with a generation count on the
>> mm or similar). I doubt we'd figure out anything that works reliably
>> and efficiently and would actually show any problems
>
> Would it be enough to simply print out a warning if we fault
> on the same address twice (or three times) in a row, and then
> flush the local TLB?
>
> I realize this would not just trigger on CPUs that fail to
> invalidate TLB entries that cause faults, but also on kernel
> paths that cause a page fault to be re-taken...

I'm actually curious if the architecture docs/software developer
manuals for IA-32 mandate any TLB invalidations on a #PF

Is there any official vendor documentation on the subject?

And perhaps equally valid, should we trust it if it exists?

> ... but then again, don't we want to find those paths and
> fix them, anyway? :)
>
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