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    SubjectRe: Interaction between Xen and XFS: stray RW mappings
    Date
    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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