Re: [PATCH v2 65/66] KVM: nSVM: Advertise and enable NRIPS for L1 iff nrips is enabled

Vitaly Kuznetsov
2020-03-03T16:14:20Z

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Set NRIPS in KVM capabilities if and only if nrips=true, which naturally
> incorporates the boot_cpu_has() check, and set nrips_enabled only if the
> KVM capability is enabled.
>
> Note, previously KVM would set nrips_enabled based purely on userspace
> input, but at worst that would cause KVM to propagate garbage into L1,
> i.e. userspace would simply be hosing its VM.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/svm.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 8e39dcd3160d..32d9c13ec6b9 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1377,7 +1377,7 @@ static __init void svm_set_cpu_caps(void)
> if (nested) {
> kvm_cpu_cap_set(X86_FEATURE_SVM);
>
> - if (boot_cpu_has(X86_FEATURE_NRIPS))
> + if (nrips)
> kvm_cpu_cap_set(X86_FEATURE_NRIPS);
>
> if (npt_enabled)
> @@ -6031,7 +6031,8 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu)
> boot_cpu_has(X86_FEATURE_XSAVES);
>
> /* Update nrips enabled cache */
> - svm->nrips_enabled = !!guest_cpuid_has(&svm->vcpu, X86_FEATURE_NRIPS);
> + svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
> + guest_cpuid_has(&svm->vcpu, X86_FEATURE_NRIPS);
>
> if (!kvm_vcpu_apicv_active(vcpu))
> return;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly