linux-kernel - [PATCH v5 6/9] x86/bugs: KVM: Move VM_CLEAR_CPU_BUFFERS into SVM as SVM_CLEAR_CPU

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Message-ID: <20251113233746.1703361-7-seanjc@google.com>
Date: Thu, 13 Nov 2025 15:37:43 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>, 
	Josh Poimboeuf <jpoimboe@...nel.org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH v5 6/9] x86/bugs: KVM: Move VM_CLEAR_CPU_BUFFERS into SVM as SVM_CLEAR_CPU_BUFFERS

Now that VMX encodes its own sequence for clearing CPU buffers, move
VM_CLEAR_CPU_BUFFERS into SVM to minimize the chances of KVM botching a
mitigation in the future, e.g. using VM_CLEAR_CPU_BUFFERS instead of
checking multiple mitigation flags.

No functional change intended.

Reviewed-by: Brendan Jackman <jackmanb@...gle.com>
Acked-by: Borislav Petkov (AMD) <bp@...en8.de>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/nospec-branch.h | 3 ---
 arch/x86/kvm/svm/vmenter.S           | 6 ++++--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index b1b1811216c5..3a5ac39877a0 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -324,9 +324,6 @@
 #define CLEAR_CPU_BUFFERS \
 	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF
 
-#define VM_CLEAR_CPU_BUFFERS \
-	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF_VM
-
 #ifdef CONFIG_X86_64
 .macro CLEAR_BRANCH_HISTORY
 	ALTERNATIVE "", "call clear_bhb_loop", X86_FEATURE_CLEAR_BHB_LOOP
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 98bfa2e00d88..3392bcadfb89 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -116,6 +116,8 @@
 	jmp 901b
 .endm
 
+#define SVM_CLEAR_CPU_BUFFERS \
+	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF_VM
 
 /**
  * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
@@ -194,7 +196,7 @@ SYM_FUNC_START(__svm_vcpu_run)
 	mov VCPU_RDI(%_ASM_DI), %_ASM_DI
 
 	/* Clobbers EFLAGS.ZF */
-	VM_CLEAR_CPU_BUFFERS
+	SVM_CLEAR_CPU_BUFFERS
 
 	/* Enter guest mode */
 3:	vmrun %_ASM_AX
@@ -366,7 +368,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	mov KVM_VMCB_pa(%rax), %rax
 
 	/* Clobbers EFLAGS.ZF */
-	VM_CLEAR_CPU_BUFFERS
+	SVM_CLEAR_CPU_BUFFERS
 
 	/* Enter guest mode */
 1:	vmrun %rax
-- 
2.52.0.rc1.455.g30608eb744-goog