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xen-devel
[Xen-devel] Re: Interaction between Xen and XFS: stray RW mappings
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To: |
Andi Kleen <andi@xxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: Interaction between Xen and XFS: stray RW mappings |
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From: |
Nick Piggin <nickpiggin@xxxxxxxxxxxx> |
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Date: |
Mon, 15 Oct 2007 21:28:10 +1000 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, David Chinner <dgc@xxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Morten Bøgeskov <xen-users@xxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, Mark Williamson <mark.williamson@xxxxxxxxxxxx> |
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Mon, 15 Oct 2007 04:29:08 -0700 |
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On Monday 15 October 2007 21:07, Andi Kleen wrote:
> On Tue, Oct 16, 2007 at 12:56:46AM +1000, Nick Piggin wrote:
> > Is this true even if you don't write through those old mappings?
>
> I think it happened for reads too. It is a little counter intuitive
> because in theory the CPU doesn't need to write back non dirty lines,
> but in the one case which took so long to debug exactly this happened
> somehow.
>
> At it is undefined for reads and writes in the architecture so
> better be safe than sorry.
Yes, typo. I meant reads or writes.
> And x86 CPUs are out of order and do speculative executation
> and that can lead to arbitary memory accesses even if the code
> never touches an particular address.
>
> Newer Intel CPUs have something called self-snoop which was supposed
> to handle this; but in some situations it doesn't seem to catch it
> either.
Fair enough, so we have to have this lazy tlb flush hook for
Xen/PAT/etc. I don't think it should be much problem to
implement.
> > Is DRM or AGP then not also broken with lazy highmem flushing, or
> > how do they solve that?
>
> AGP doesn't allocate highmem pages. Not sure about the DRM code.
Hmm, OK. It looks like DRM vmallocs memory (which gives highmem).
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