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SubjectRe: [PATCH] KVM: SVM: Add a dedicated INVD intercept routine
Date
Tom Lendacky <thomas.lendacky@amd.com> writes:

> From: Tom Lendacky <thomas.lendacky@amd.com>
>
> The INVD instruction intercept performs emulation. Emulation can't be done
> on an SEV guest because the guest memory is encrypted.
>
> Provide a dedicated intercept routine for the INVD intercept. Within this
> intercept routine just skip the instruction for an SEV guest, since it is
> emulated as a NOP anyway.
>
> Fixes: 1654efcbc431 ("KVM: SVM: Add KVM_SEV_INIT command")
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/kvm/svm/svm.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index c91acabf18d0..332ec4425d89 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2183,6 +2183,17 @@ static int iret_interception(struct vcpu_svm *svm)
> return 1;
> }
>
> +static int invd_interception(struct vcpu_svm *svm)
> +{
> + /*
> + * Can't do emulation on an SEV guest and INVD is emulated
> + * as a NOP, so just skip the instruction.
> + */
> + return (sev_guest(svm->vcpu.kvm))
> + ? kvm_skip_emulated_instruction(&svm->vcpu)
> + : kvm_emulate_instruction(&svm->vcpu, 0);
> +}
> +
> static int invlpg_interception(struct vcpu_svm *svm)
> {
> if (!static_cpu_has(X86_FEATURE_DECODEASSISTS))
> @@ -2774,7 +2785,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
> [SVM_EXIT_RDPMC] = rdpmc_interception,
> [SVM_EXIT_CPUID] = cpuid_interception,
> [SVM_EXIT_IRET] = iret_interception,
> - [SVM_EXIT_INVD] = emulate_on_interception,
> + [SVM_EXIT_INVD] = invd_interception,
> [SVM_EXIT_PAUSE] = pause_interception,
> [SVM_EXIT_HLT] = halt_interception,
> [SVM_EXIT_INVLPG] = invlpg_interception,

Out of pure curiosity,

does it sill make sense to intercept INVD when we just skip it? Would it
rather make sense to disable INVD intercept for SEV guests completely?

--
Vitaly

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