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

Like Xu
2021-03-04T03:45:42Z

On 2021/3/4 2:03, Sean Christopherson wrote:
> On Wed, Mar 03, 2021, Like Xu wrote:
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 034708a3df20..ec4593e0ee6d 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -7268,6 +7268,8 @@ static __init void vmx_set_cpu_caps(void)
>> supported_xss = 0;
>> if (!cpu_has_vmx_xsaves())
>> kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>> + else if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
>> + supported_xss |= XFEATURE_MASK_LBR;
>>
>> /* CPUID 0x80000001 */
>> if (!cpu_has_vmx_rdtscp())
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index d773836ceb7a..bca2e318ff24 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -10433,6 +10433,8 @@ int kvm_arch_hardware_setup(void *opaque)
>>
>> if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
>> supported_xss = 0;
>> + else
>> + supported_xss &= host_xss;
>
> Not your fault by any means, but I would prefer to have matching logic for XSS
> and XCR0. The existing clearing of supported_xss here is pointless. E.g. I'd
> prefer something like the following, though Paolo may have a different opinion.

I have no preference for where to do rdmsrl() in kvm_arch_init()
or kvm_arch_hardware_setup().

It's true the assignment of supported_xss in the kvm/intel
tree is redundant and introducing KVM_SUPPORTED_XSS is also fine to me.

>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 6d7e760fdfa0..c781034463e5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7244,12 +7244,15 @@ static __init void vmx_set_cpu_caps(void)
> kvm_cpu_cap_clear(X86_FEATURE_INVPCID);
> if (vmx_pt_mode_is_host_guest())
> kvm_cpu_cap_check_and_set(X86_FEATURE_INTEL_PT);
> + if (!cpu_has_vmx_arch_lbr()) {
> + kvm_cpu_cap_clear(X86_FEATURE_ARCH_LBR);
> + supported_xss &= ~XFEATURE_MASK_LBR;
> + }
>

I will move the above part to the LBR patch
and leave the left part as a pre-patch for Paolo's review.

> 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;
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
>