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    SubjectRe: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)
    On Mon, Aug 20, 2018 at 03:27:52PM -0700, Linus Torvalds wrote:
    > On Mon, Aug 20, 2018 at 3:02 PM Woodhouse, David <dwmw@amazon.co.uk> wrote:
    > >
    > > It's the *kernel* we don't want being able to access those pages,
    > > because of the multitude of unfixable cache load gadgets.
    >
    > Ahh.
    >
    > I guess the proof is in the pudding. Did somebody try to forward-port
    > that patch set and see what the performance is like?
    >
    > It used to be just 500 LOC. Was that because they took horrible
    > shortcuts? Are the performance numbers for the 32-bit case that
    > already had the kmap() overhead?

    The last version I worked on was a bit before Meltdown was public:
    https://lkml.org/lkml/2017/9/7/445

    The overhead was a lot, but Dave Hansen gave some ideas about how to
    speed things up in this thread: https://lkml.org/lkml/2017/9/20/828

    Since meltdown hit, I haven't worked seriously on understand and
    implementing his suggestions, in part because it wasn't clear to me
    what pieces of the infrastructure we might be able to re-use. Someone
    who knows more about mm/ might be able to suggest an approach, though.

    Tycho

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