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Re: [Xen-devel] [PATCH for-4.5] x86/HVM: Partial revert of 28b4baacd5

>>> On 25.11.14 at 11:08, <andrew.cooper3@xxxxxxxxxx> wrote:
> A failed vmentry is overwhelmingly likely to be caused by corrupt VMCS state.
> As a result, injecting a fault and retrying the the vmentry is likely to 
> fail
> in the same way.

That's not all that unlikely - remember that the change was prompted
by the XSA-110 fix. There CS pieces being in a bad state would get
corrected by the exception injection.

> One other alternative, which I would pursue if we were not already in -rc2
> would be to add some extra logic to detect repeated vmentry failure and 
> allow
> one attempt to shoot userspace before giving up and crashing the domain.

That's not even needed afaict (and if it really is, it can't be all that
difficult/intrusive): Did you observe what you attempt to fix here in
practice, or is this just from theoretical considerations? I ask because
I don't think it can actually happen, as the second time we get here
the guest ought to be in kernel mode (due to the exception injection)
and hence would get crashed anyway.


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