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SubjectRe: [RFC PATCH 28/35] KVM: X86: Update kvm_skip_emulated_instruction() for an SEV-ES guest
On Mon, Sep 14, 2020 at 03:15:42PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
>
> The register state for an SEV-ES guest is encrypted so the value of the
> RIP cannot be updated. For an automatic exit, the RIP will be advanced
> as necessary. For a non-automatic exit, it is up to the #VC handler in
> the guest to advance the RIP.
>
> Add support to skip any RIP updates in kvm_skip_emulated_instruction()
> for an SEV-ES guest.

Is there a reason this can't be handled in svm? E.g. can KVM be reworked
to effectively split the emulation logic so that it's a bug for KVM to end
up trying to modify RIP?

Also, patch 06 modifies SVM's skip_emulated_instruction() to skip the RIP
update, but keeps the "svm_set_interrupt_shadow(vcpu, 0)" logic. Seems like
either that change or this one is wrong.

> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/kvm/x86.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 23564d02d158..1dbdca607511 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6874,13 +6874,17 @@ static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu)
>
> int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
> {
> - unsigned long rflags = kvm_x86_ops.get_rflags(vcpu);
> + unsigned long rflags;
> int r;
>
> r = kvm_x86_ops.skip_emulated_instruction(vcpu);
> if (unlikely(!r))
> return 0;
>
> + if (vcpu->arch.vmsa_encrypted)
> + return 1;
> +
> + rflags = kvm_x86_ops.get_rflags(vcpu);
> /*
> * rflags is the old, "raw" value of the flags. The new value has
> * not been saved yet.
> --
> 2.28.0
>

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