Re: [PATCH v3 08/21] KVM:x86: Init kvm_caps.supported_xss with supported feature bits

Chao Gao
2023-06-06T08:38:35Z

On Thu, May 11, 2023 at 12:08:44AM -0400, Yang Weijiang wrote:
>Initialize kvm_caps.supported_xss with host XSS msr value AND XSS mask.
>KVM_SUPPORTED_XSS holds all potential supported feature bits,

>the result
>represents all KVM supported feature bits which is used for swapping guest
>and host FPU contents.

do you mean kvm_caps.supported_xss by "the result"? I don't see how
fpu_swap_kvm_fpstate() uses kvm_caps.supported_xss.

>
>Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>---
> arch/x86/kvm/vmx/vmx.c | 1 -
> arch/x86/kvm/x86.c | 6 +++++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index 44fb619803b8..c872a5aafa50 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -7806,7 +7806,6 @@ static __init void vmx_set_cpu_caps(void)
> kvm_cpu_cap_set(X86_FEATURE_UMIP);
>
> /* CPUID 0xD.1 */
>- kvm_caps.supported_xss = 0;

AMD has the same statement. Do you need to remove that one?

> if (!cpu_has_vmx_xsaves())
> kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index ab3360a10933..d2975ca96ac5 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -223,6 +223,8 @@ 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);
>
>@@ -9472,8 +9474,10 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>
> 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(ops->pmu_ops);
>
>--
>2.27.0
>