linux-kernel - Re: [PATCH v3 08/21] KVM:x86: Init kvm_caps.supported

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Date:   Tue, 6 Jun 2023 16:38:11 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <rppt@...nel.org>, <binbin.wu@...ux.intel.com>,
        <rick.p.edgecombe@...el.com>, <john.allen@....com>
Subject: Re: [PATCH v3 08/21] KVM:x86: Init kvm_caps.supported_xss with
 supported feature bits

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@...el.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
>