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

Sean Christopherson
2023-01-27T21:46:13Z

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
>