From: Sean Christopherson <seanjc@google.com>
Date: Tue, 10 Mar 2026 22:04:14 +0000 (-0700)
Subject: KVM: SVM: Add a helper to get LBR field pointer to dedup MSR accesses
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0b4a043a54144aef3e5a2597c29c6adb5e6c47dc;p=thirdparty%2Fkernel%2Flinux.git

KVM: SVM: Add a helper to get LBR field pointer to dedup MSR accesses

Add a helper to get a pointer to the corresponding VMCB field given an LBR
MSR index, and use it to dedup the handling in svm_{g,s}et_msr().

No functional change intended.

Suggested-by: Yosry Ahmed <yosry@kernel.org>
Reviewed-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260310220414.2569208-1-seanjc@google.com
[sean: use KVM_BUG_ON() instead of BUILD_BUG(), clang ain't smart enough]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 4bf0f5d7167fa..5e6bd7fca2982 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2751,6 +2751,24 @@ static int svm_get_feature_msr(u32 msr, u64 *data)
 	return 0;
 }
 
+static u64 *svm_vmcb_lbr(struct vcpu_svm *svm, u32 msr)
+{
+	switch (msr) {
+	case MSR_IA32_LASTBRANCHFROMIP:
+		return &svm->vmcb->save.br_from;
+	case MSR_IA32_LASTBRANCHTOIP:
+		return &svm->vmcb->save.br_to;
+	case MSR_IA32_LASTINTFROMIP:
+		return &svm->vmcb->save.last_excp_from;
+	case MSR_IA32_LASTINTTOIP:
+		return &svm->vmcb->save.last_excp_to;
+	default:
+		break;
+	}
+	KVM_BUG_ON(1, svm->vcpu.kvm);
+	return &svm->vmcb->save.br_from;
+}
+
 static bool sev_es_prevent_msr_access(struct kvm_vcpu *vcpu,
 				      struct msr_data *msr_info)
 {
@@ -2827,16 +2845,10 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = lbrv ? svm->vmcb->save.dbgctl : 0;
 		break;
 	case MSR_IA32_LASTBRANCHFROMIP:
-		msr_info->data = lbrv ? svm->vmcb->save.br_from : 0;
-		break;
 	case MSR_IA32_LASTBRANCHTOIP:
-		msr_info->data = lbrv ? svm->vmcb->save.br_to : 0;
-		break;
 	case MSR_IA32_LASTINTFROMIP:
-		msr_info->data = lbrv ? svm->vmcb->save.last_excp_from : 0;
-		break;
 	case MSR_IA32_LASTINTTOIP:
-		msr_info->data = lbrv ? svm->vmcb->save.last_excp_to : 0;
+		msr_info->data = lbrv ? *svm_vmcb_lbr(svm, msr_info->index) : 0;
 		break;
 	case MSR_VM_HSAVE_PA:
 		msr_info->data = svm->nested.hsave_msr;
@@ -3112,35 +3124,14 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		svm_update_lbrv(vcpu);
 		break;
 	case MSR_IA32_LASTBRANCHFROMIP:
-		if (!lbrv)
-			return KVM_MSR_RET_UNSUPPORTED;
-		if (!msr->host_initiated)
-			return 1;
-		svm->vmcb->save.br_from = data;
-		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
-		break;
 	case MSR_IA32_LASTBRANCHTOIP:
-		if (!lbrv)
-			return KVM_MSR_RET_UNSUPPORTED;
-		if (!msr->host_initiated)
-			return 1;
-		svm->vmcb->save.br_to = data;
-		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
-		break;
 	case MSR_IA32_LASTINTFROMIP:
-		if (!lbrv)
-			return KVM_MSR_RET_UNSUPPORTED;
-		if (!msr->host_initiated)
-			return 1;
-		svm->vmcb->save.last_excp_from = data;
-		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
-		break;
 	case MSR_IA32_LASTINTTOIP:
 		if (!lbrv)
 			return KVM_MSR_RET_UNSUPPORTED;
 		if (!msr->host_initiated)
 			return 1;
-		svm->vmcb->save.last_excp_to = data;
+		*svm_vmcb_lbr(svm, ecx) = data;
 		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
 		break;
 	case MSR_VM_HSAVE_PA: