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

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Message-ID: <20251106101138.2756175-1-binbin.wu@linux.intel.com>
Date: Thu,  6 Nov 2025 18:11:38 +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,
	binbin.wu@...ux.intel.com
Subject: [PATCH] KVM: x86: Add a help 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 by passing XCR0 and XSS values accordingly.

No functional change intended.

Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
---
The patch is based on the patch series
"KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling" [1], which is applied on 
top of kvm-x86 next branch(commit a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a).

[1] https://lore.kernel.org/all/20251030224246.3456492-1-seanjc@google.com
---
 arch/x86/kvm/x86.c | 25 +++++--------------------
 1 file changed, 5 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b8df02a083b2..35fc1333e198 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1203,33 +1203,18 @@ 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, u64 xcr0, u64 xss)
 {
 	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);
+			xsetbv(XCR_XFEATURE_ENABLED_MASK, 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)
-		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 (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
-		    vcpu->arch.ia32_xss != kvm_host.xss)
-			wrmsrq(MSR_IA32_XSS, kvm_host.xss);
+			wrmsrq(MSR_IA32_XSS, xss);
 	}
 }
 
@@ -11310,7 +11295,7 @@ 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, vcpu->arch.xcr0, vcpu->arch.ia32_xss);
 
 	if (unlikely(vcpu->arch.switch_db_regs &&
 		     !(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH))) {
@@ -11406,7 +11391,7 @@ 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, kvm_host.xcr0, kvm_host.xss);
 
 	/*
 	 * Sync xfd before calling handle_exit_irqoff() which may

base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
-- 
2.46.0