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SubjectRe: [PATCH 1/9] KVM: SVM: Never reject emulation due to SMAP errata for !SEV guests
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On 20/01/2022 01:07, Sean Christopherson wrote:
> Always signal that emulation is possible for !SEV guests regardless of
> whether or not the CPU provided a valid instruction byte stream. KVM can
> read all guest state (memory and registers) for !SEV guests, i.e. can
> fetch the code stream from memory even if the CPU failed to do so because
> of the SMAP errata.
>
> Fixes: 05d5a4863525 ("KVM: SVM: Workaround errata#1096 (insn_len maybe zero on SMAP violation)")
> 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 | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 6d31d357a83b..aa1649b8cd8f 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4257,8 +4257,13 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i
> bool smep, smap, is_user;
> unsigned long cr4;
>
> + /* Emulation is always possible when KVM has access to all guest state. */
> + if (!sev_guest(vcpu->kvm))
> + return true;
> +
> /*
> - * When the guest is an SEV-ES guest, emulation is not possible.
> + * Emulation is impossible for SEV-ES guests as KVM doesn't have access
> + * to guest register state.
> */
> if (sev_es_guest(vcpu->kvm))
> return false;
> @@ -4318,9 +4323,6 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i
> smap = cr4 & X86_CR4_SMAP;
> is_user = svm_get_cpl(vcpu) == 3;
> if (smap && (!smep || is_user)) {
> - if (!sev_guest(vcpu->kvm))
> - return true;
> -
> pr_err_ratelimited("KVM: SEV Guest triggered AMD Erratum 1096\n");
> kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> }

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