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SubjectRe: [PATCH 2/2] KVM: SVM: Emulate next_rip svm feature
On Wed, Jul 28, 2010 at 07:57:36AM -0400, Avi Kivity wrote:

> If the instruction opcode is on mmio, the processor never sees the
> opcode and thus can not intercept. Or the processor may see one
> instruction, which is not intercepted, but by the time the emulator
> kicks in a different instruction takes its place, since another vcpu is
> evilly cross-modifying the code.

Right. X-modifying code is a problem too.

> The guest (L2 in this case) is doomed since it execution cannot
> continue. But L1 and L0 are fine. The problem with L2 avoiding
> intercepts is that L2 can change control registers and take over L1.

Right too. We can not ignore it. The right fix is probably a check for
the instruction intercepts right after the decoder has run and before
the emulator ran.


Joerg Roedel - AMD Operating System Research Center

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