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SubjectRe: [PATCH 3/9] KVM: SVM: Don't intercept #GP for SEV guests
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On 20/01/2022 01:07, Sean Christopherson wrote:
> Never intercept #GP for SEV guests as reading SEV guest private memory
> will return cyphertext, i.e. emulating on #GP can't work as intended.
>

"ciphertext" seems to be the convention.


> Cc: stable@vger.kernel.org
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Liam Merwick <liam.merwick@oracle.com>

> ---
> arch/x86/kvm/svm/svm.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 85703145eb0a..edea52be6c01 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -312,7 +312,11 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
> return ret;
> }
>
> - if (svm_gp_erratum_intercept)
> + /*
> + * Never intercept #GP for SEV guests, KVM can't
> + * decrypt guest memory to workaround the erratum.
> + */
> + if (svm_gp_erratum_intercept && !sev_guest(vcpu->kvm))
> set_exception_intercept(svm, GP_VECTOR);
> }
> }
> @@ -1010,9 +1014,10 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
> * Guest access to VMware backdoor ports could legitimately
> * trigger #GP because of TSS I/O permission bitmap.
> * We intercept those #GP and allow access to them anyway
> - * as VMware does.
> + * as VMware does. Don't intercept #GP for SEV guests as KVM can't
> + * decrypt guest memory to decode the faulting instruction.
> */
> - if (enable_vmware_backdoor)
> + if (enable_vmware_backdoor && !sev_guest(vcpu->kvm))
> set_exception_intercept(svm, GP_VECTOR);
>
> svm_set_intercept(svm, INTERCEPT_INTR);

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