On 9/9/2025 5:39 PM, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
>
> Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
> XSAVES is supported. host_xss contains the host supported xstate feature
> bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
> enabled XSS feature bits, the resulting value represents the supervisor
> xstates that are available to guest and are backed by host FPU framework
> for swapping {guest,host} XSAVE-managed registers/MSRs.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
> arch/x86/kvm/x86.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbae3bf405c7..c15e8c00dc7d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -220,6 +220,8 @@ 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
> +
(related to my comment on previous patch)
It seems better to move the comment about Intel PT (IA32_XSS[bit 8]) in
kvm_set_msr_common() to above KVM_SUPPORTED_XSS.
> bool __read_mostly allow_smaller_maxphyaddr = 0;
> EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
>
> @@ -9789,14 +9791,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
> kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;
> }
> +
> + if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> + rdmsrq(MSR_IA32_XSS, kvm_host.xss);
> + kvm_caps.supported_xss = kvm_host.xss & KVM_SUPPORTED_XSS;
> + }
> +
> kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;
> kvm_caps.inapplicable_quirks = KVM_X86_CONDITIONAL_QUIRKS;
>
> rdmsrq_safe(MSR_EFER, &kvm_host.efer);
>
> - if (boot_cpu_has(X86_FEATURE_XSAVES))
> - rdmsrq(MSR_IA32_XSS, kvm_host.xss);
> -
> kvm_init_pmu_capability(ops->pmu_ops);
>
> if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))