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SubjectRe: [PATCH 2/3] KVM: SVM: Restore correct registers after sel_cr0 intercept emulation
On Thu, Sep 02, 2010 at 12:02:02PM -0400, Avi Kivity wrote:
> On 09/02/2010 06:29 PM, Joerg Roedel wrote:
> > This patch implements restoring of the correct rip, rsp, and
> > rax after the svm emulation in KVM injected a selective_cr0
> > write intercept into the guest hypervisor. The problem was
> > that the vmexit is emulated in the instruction emulation
> > which later commits the registers right after the write-cr0
> > instruction. So the l1 guest will continue to run with the
> > l2 rip, rsp and rax resulting in unpredictable behavior.
>
> Please post a unit test for this.

Will do. Should be an easy test.

> > This patch is not the final word, it is just an easy patch
> > to fix the issue. The real fix will be done when the
> > instruction emulator is made aware of nested virtualization.
> > Until this is done this patch fixes the issue and provides
> > an easy way to fix this in -stable too.
>
> I agree. We can probably use X86EMUL_PROPAGATE_FAULT to abort
> emulation, but looking at the code, it will take some refactoring.

I thought of an X86EMUL_INTERCEPTED. An architecture specific function
is called after instruction decoding which checks if an intercept is
necessary. If it returns X86EMUL_INTERCEPTED then the instruction
emulation is discarded and kvm goes straight back into the guest.


Joerg

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