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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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