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x86/bugs: KVM: Move VM_CLEAR_CPU_BUFFERS into SVM as SVM_CLEAR_CPU_BUFFERS

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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@google.com>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251113233746.1703361-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-11-13 15:37:43 -08:00
parent e6ff1d61de
commit fc704b5789
2 changed files with 4 additions and 5 deletions
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3
arch/x86/include/asm/nospec-branch.h
View File

@ -329,9 +329,6 @@
#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

6
arch/x86/kvm/svm/vmenter.S
View File

@ -92,6 +92,8 @@
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
@ -170,7 +172,7 @@ 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
@ -339,7 +341,7 @@ 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