Re: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

Vitaly Kuznetsov
2020-03-03T16:12:10Z

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

> Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
> shouldn't advertise features that realistically can't be used. Use
> kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
> svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
> adjustments into common x86 code.
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/svm.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f32fc3c03667..8e39dcd3160d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
> if (avic)
> kvm_cpu_cap_clear(X86_FEATURE_X2APIC);
>
> - /* CPUID 0x80000001 */
> - if (nested)
> + /* CPUID 0x80000001 and 0x8000000A (SVM features) */
> + if (nested) {
> kvm_cpu_cap_set(X86_FEATURE_SVM);
>
> + if (boot_cpu_has(X86_FEATURE_NRIPS))
> + kvm_cpu_cap_set(X86_FEATURE_NRIPS);
> +
> + if (npt_enabled)
> + kvm_cpu_cap_set(X86_FEATURE_NPT);
> + }
> +
> /* CPUID 0x80000008 */
> if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
> boot_cpu_has(X86_FEATURE_AMD_SSBD))
> kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
> -
> - /* CPUID 0x8000000A */
> - /* Support next_rip if host supports it */
> - kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
> -
> - if (npt_enabled)
> - kvm_cpu_cap_set(X86_FEATURE_NPT);
> }
>
> static __init int svm_hardware_setup(void)
> @@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
> {
> switch (entry->function) {
> case 0x8000000A:
> + if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
> + entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> + break;
> + }
> entry->eax = 1; /* SVM revision 1 */
> entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
> ASID emulation to nested SVM */

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

--
Vitaly