Re: [PATCH] KVM: SVM: fix random segfaults with NPT enabled

Joerg Rodel
2008-08-27T13:58:28Z

On Wed, Aug 27, 2008 at 04:53:26PM +0300, Avi Kivity wrote:
> Avi Kivity wrote:
> >Joerg Rodel wrote:
> >>From: Joerg Roedel <joerg.roedel@amd.com>
> >>
> >>This patch introduces a guest TLB flush on every NPF exit in KVM. This fixes
> >>random segfaults and #UD exceptions in the guest seen under some workloads
> >>(e.g. long running compile workloads or tbench). A kernbench run with and
> >>without that fix showed that it has a slowdown lower than 0.5%
> >>
> >>
> >
> >hm. tbench doesn't allocate memory, so there shouldn't be any npt faults. I don't
> >see how this can make a difference.
> >
> >It can only change something if X is started and we're tracking writes to the
> >framebuffer. Is this the case?
> >
>
> I fixed a missing flush in this area. Does it help? (I doubt it). Can you post
> instructions on how to reproduce?

I will test it. Is the fix in your latest kernel.org tree? Reproduce it
with a KVM guest and start tbench in it with around 100 clients
configured. The tbench-process will crash when the bug is hit.

Joerg

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