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SubjectRe: [PATCH] KVM: nSVM: check for EFER.SVME=1 before entering guest
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On 3/18/20 5:41 AM, Paolo Bonzini wrote:
> EFER is set for L2 using svm_set_efer, which hardcodes EFER_SVME to 1 and hides
> an incorrect value for EFER.SVME in the L1 VMCB. Perform the check manually
> to detect invalid guest state.
>
> Reported-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/svm.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 08568ae9f7a1..2125c6ae5951 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3558,6 +3558,9 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
>
> static bool nested_vmcb_checks(struct vmcb *vmcb)
> {
> + if ((vmcb->save.efer & EFER_SVME) == 0)
> + return false;
> +
> if ((vmcb->control.intercept & (1ULL << INTERCEPT_VMRUN)) == 0)
> return false;
>

Ah! This now tells me that I forgot the KVM fix that was supposed to
accompany my patchset.

Do we need this check in software ? I wasn't checking the bit in KVM and
instead I was just making sure that L0 sets that bit based on the
setting in nested vmcb:


+static void nested_svm_set_efer(struct kvm_vcpu *vcpu, u64
nested_vmcb_efer)
+{
+       svm_set_efer(vcpu, nested_vmcb_efer);
+
+       if (!(nested_vmcb_efer & EFER_SVME))
+               to_svm(vcpu)->vmcb->save.efer &= ~EFER_SVME;
+}
+
 static int is_external_interrupt(u32 info)
 {
        info &= SVM_EVTINJ_TYPE_MASK | SVM_EVTINJ_VALID;
@@ -3554,7 +3562,7 @@ static void enter_svm_guest_mode(struct vcpu_svm
*svm, u64
        svm->vmcb->save.gdtr = nested_vmcb->save.gdtr;
        svm->vmcb->save.idtr = nested_vmcb->save.idtr;
        kvm_set_rflags(&svm->vcpu, nested_vmcb->save.rflags);
-       svm_set_efer(&svm->vcpu, nested_vmcb->save.efer);
+       nested_svm_set_efer(&svm->vcpu, nested_vmcb->save.efer);
        svm_set_cr0(&svm->vcpu, nested_vmcb->save.cr0);
        svm_set_cr4(&svm->vcpu, nested_vmcb->save.cr4);
        if (npt_enabled) {
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