linux-kernel - [PATCH v2] KVM: x86: Add a helper to dedup loading guest/host XCR0 and XSS

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Message-ID: <20251110050539.3398759-1-binbin.wu@linux.intel.com>
Date: Mon, 10 Nov 2025 13:05:39 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: seanjc@...gle.com,
	pbonzini@...hat.com
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	chao.gao@...el.com,
	xiaoyao.li@...el.com,
	binbin.wu@...ux.intel.com
Subject: [PATCH v2] KVM: x86: Add a helper to dedup loading guest/host XCR0 and XSS

Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
guest/host xfeatures.

Opportunistically return early if X86_CR4_OSXSAVE is not set to reduce
indentations.

No functional change intended.

Suggested-by: Chao Gao <chao.gao@...el.com>
Reviewed-by: Chao Gao <chao.gao@...el.com>
Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
---
v2:
- Pass a bool to distinguish guest/host. [Chao, Xiaoyao]
- Fix a typo in the short log. [Chao]
- Opportunistically return early if X86_CR4_OSXSAVE is not set to reduce
  indentations.

v1:
- https://lore.kernel.org/kvm/20251106101138.2756175-1-binbin.wu@linux.intel.com
---
 arch/x86/kvm/x86.c | 33 ++++++++++-----------------------
 1 file changed, 10 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9c2e28028c2b..2c521902e2c6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1219,34 +1219,21 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_lmsw);
 
-static void kvm_load_guest_xfeatures(struct kvm_vcpu *vcpu)
+static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
 {
 	if (vcpu->arch.guest_state_protected)
 		return;
 
-	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
-		if (vcpu->arch.xcr0 != kvm_host.xcr0)
-			xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
-
-		if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
-		    vcpu->arch.ia32_xss != kvm_host.xss)
-			wrmsrq(MSR_IA32_XSS, vcpu->arch.ia32_xss);
-	}
-}
-
-static void kvm_load_host_xfeatures(struct kvm_vcpu *vcpu)
-{
-	if (vcpu->arch.guest_state_protected)
+	if (!kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE))
 		return;
 
-	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
-		if (vcpu->arch.xcr0 != kvm_host.xcr0)
-			xsetbv(XCR_XFEATURE_ENABLED_MASK, kvm_host.xcr0);
+	if (vcpu->arch.xcr0 != kvm_host.xcr0)
+		xsetbv(XCR_XFEATURE_ENABLED_MASK,
+		       load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0);
 
-		if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
-		    vcpu->arch.ia32_xss != kvm_host.xss)
-			wrmsrq(MSR_IA32_XSS, kvm_host.xss);
-	}
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
+	    vcpu->arch.ia32_xss != kvm_host.xss)
+		wrmsrq(MSR_IA32_XSS, load_guest ? vcpu->arch.ia32_xss : kvm_host.xss);
 }
 
 static void kvm_load_guest_pkru(struct kvm_vcpu *vcpu)
@@ -11333,7 +11320,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.guest_fpu.xfd_err)
 		wrmsrq(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
 
-	kvm_load_guest_xfeatures(vcpu);
+	kvm_load_xfeatures(vcpu, true);
 
 	if (unlikely(vcpu->arch.switch_db_regs &&
 		     !(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH))) {
@@ -11429,7 +11416,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	vcpu->mode = OUTSIDE_GUEST_MODE;
 	smp_wmb();
 
-	kvm_load_host_xfeatures(vcpu);
+	kvm_load_xfeatures(vcpu, false);
 
 	/*
 	 * Sync xfd before calling handle_exit_irqoff() which may

base-commit: 9052f4f6c539ea1fb7b282a34e6bb33154ce0b63
-- 
2.46.0