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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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