linux-kernel - [PATCH v11 08/23] KVM: x86: Initialize kvm_caps.supported

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Message-ID: <20250704085027.182163-9-chao.gao@intel.com>
Date: Fri,  4 Jul 2025 01:49:39 -0700
From: Chao Gao <chao.gao@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	seanjc@...gle.com,
	pbonzini@...hat.com,
	dave.hansen@...el.com
Cc: rick.p.edgecombe@...el.com,
	mlevitsk@...hat.com,
	john.allen@....com,
	weijiang.yang@...el.com,
	minipli@...ecurity.net,
	xin@...or.com,
	Chao Gao <chao.gao@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v11 08/23] KVM: x86: Initialize kvm_caps.supported_xss

From: Yang Weijiang <weijiang.yang@...el.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@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Reviewed-by: Chao Gao <chao.gao@...el.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 dd984c6acae5..fcbb4566b4c6 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
+
 bool __read_mostly allow_smaller_maxphyaddr = 0;
 EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
 
@@ -9892,14 +9894,17 @@ 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))
-- 
2.47.1