Re: [PATCH v3 9/9] KVM: x86: Add XSAVE Support for Architectural LBRs

Sean Christopherson
2021-03-04T16:33:24Z

On Thu, Mar 04, 2021, Like Xu wrote:
> On 2021/3/4 2:03, Sean Christopherson wrote:
> > if (vmx_umip_emulated())
> > kvm_cpu_cap_set(X86_FEATURE_UMIP);
> >
> > /* CPUID 0xD.1 */
> > - supported_xss = 0;
> > if (!cpu_has_vmx_xsaves())
> > kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>
> if (!cpu_has_vmx_xsaves())
> supported_xss = 0;

Argh, I forgot XSAVES has a VMCS control. That's why kvm_arch_hardware_setup()
clears supported_xss if !XSAVES. I guess just leave that existing code, but
maybe add a comment.

Paolo, any thoughts on how to keep supported_xss aligned with support_xcr0,
without spreading the logic around too much?

> kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 7b0adebec1ef..5f9eb1f5b840 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -205,6 +205,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
> > | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
> > | XFEATURE_MASK_PKRU)
> >
> > +#define KVM_SUPPORTED_XSS XFEATURE_MASK_LBR
> > +
> > u64 __read_mostly host_efer;
> > EXPORT_SYMBOL_GPL(host_efer);
> >
> > @@ -8037,6 +8039,11 @@ int kvm_arch_init(void *opaque)
> > supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
> > }
> >
> > + if (boot_cpu_has(X86_FEATURE_XSAVES))
>
> {
>
> > + rdmsrl(MSR_IA32_XSS, host_xss);
> > + supported_xss = host_xss & KVM_SUPPORTED_XSS;
> > + }
> > +
> > if (pi_inject_timer == -1)
> > pi_inject_timer = housekeeping_enabled(HK_FLAG_TIMER);
> > #ifdef CONFIG_X86_64
> > @@ -10412,9 +10419,6 @@ int kvm_arch_hardware_setup(void *opaque)
> >
> > rdmsrl_safe(MSR_EFER, &host_efer);
> >
> > - if (boot_cpu_has(X86_FEATURE_XSAVES))
> > - rdmsrl(MSR_IA32_XSS, host_xss);
> > -
> > r = ops->hardware_setup();
> > if (r != 0)
> > return r;
> > @@ -10422,9 +10426,6 @@ int kvm_arch_hardware_setup(void *opaque)
> > memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
> > kvm_ops_static_call_update();
> >
> > - if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
> > - supported_xss = 0;
> > -
> > #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
> > cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
> > #undef __kvm_cpu_cap_has
> >
>