Re: [PATCH v2 09/15] KVM: x86: Refine the matching and clearing logic for supported_xss

[Sean Christopherson <seanjc@google.com>]

On Thu, Nov 24, 2022, Yang Weijiang wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> Refine the code path of the existing clearing of supported_xss in this way:
> initialize the supported_xss with the filter of KVM_SUPPORTED_XSS mask and
> update its value in a bit clear manner (rather than bit setting).
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 5 +++--
>  arch/x86/kvm/x86.c     | 6 +++++-
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9bd52ad3bbf4..2ab4c33b5008 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7738,9 +7738,10 @@ static __init void vmx_set_cpu_caps(void)
>  		kvm_cpu_cap_set(X86_FEATURE_UMIP);
>  
>  	/* CPUID 0xD.1 */
> -	kvm_caps.supported_xss = 0;

This needs to stay until VMX actually supports something.

> -	if (!cpu_has_vmx_xsaves())
> +	if (!cpu_has_vmx_xsaves()) {
>  		kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
> +		kvm_caps.supported_xss = 0;

This is already handled in common KVM.

> +	}
>  
>  	/* CPUID 0x80000001 and 0x7 (RDPID) */
>  	if (!cpu_has_vmx_rdtscp()) {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 74c858eaa1ea..889be0c9176d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -217,6 +217,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>  				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>  				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>  
> +#define KVM_SUPPORTED_XSS     0
> +
>  u64 __read_mostly host_efer;
>  EXPORT_SYMBOL_GPL(host_efer);
>  
> @@ -11999,8 +12001,10 @@ int kvm_arch_hardware_setup(void *opaque)
>  
>  	rdmsrl_safe(MSR_EFER, &host_efer);
>  
> -	if (boot_cpu_has(X86_FEATURE_XSAVES))
> +	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
>  		rdmsrl(MSR_IA32_XSS, host_xss);
> +		kvm_caps.supported_xss = host_xss & KVM_SUPPORTED_XSS;
> +	}
>  
>  	kvm_init_pmu_capability();
>  
> -- 
> 2.27.0
>