Re: [PATCH 7/7] KVM: VMX: replace vmx_spec_ctrl_restore_host with RESTORE_HOST_SPEC_CTRL_BODY

[Chang S. Bae]

On 4/8/2026 2:48 PM, Paolo Bonzini wrote:
> On 4/8/26 20:22, Paolo Bonzini wrote:
> >   #ifdef CONFIG_X86_64
> >       mov PER_CPU_VAR(x86_spec_ctrl_current), %rdx
> >       cmp \guest_spec_ctrl, %rdx
> > -    je \label
> > +    ALTERNATIVE "", __stringify(je \label), X86_FEATURE_KERNEL_IBRS
>
> Actually the other way round:
>
>          ALTERNATIVE __stringify(je \label), "", X86_FEATURE_KERNEL_IBRS

Also, that CMP appears unnecessary with X86_FEATURE_KERNEL_IBRS. Maybe 
something like the attached diff is possible.

Thanks,
CHang

diff --git a/arch/x86/kvm/vmenter.h b/arch/x86/kvm/vmenter.h
index e17aedc37187..c67ec56d5110 100644
--- a/arch/x86/kvm/vmenter.h
+++ b/arch/x86/kvm/vmenter.h
@@ -54,20 +54,23 @@
 	/* Now restore the host value of the MSR if different from the guest's.  */
 #ifdef CONFIG_X86_64
 	mov PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+	ALTERNATIVE "", __stringify(jmp 999f), X86_FEATURE_KERNEL_IBRS
 	cmp \guest_spec_ctrl, %rdx
-	ALTERNATIVE __stringify(je \label), "", X86_FEATURE_KERNEL_IBRS
+	je \label
 	movl %edx, %eax
 	shr $32, %rdx
 #else
 	mov PER_CPU_VAR(x86_spec_ctrl_current), %eax
+	mov PER_CPU_VAR(x86_spec_ctrl_current + 4), %edx
+	ALTERNATIVE "", __stringify(jmp 999f), X86_FEATURE_KERNEL_IBRS
 	mov \guest_spec_ctrl, %esi
 	xor %eax, %esi
-	mov PER_CPU_VAR(x86_spec_ctrl_current + 4), %edx
 	mov 4 + \guest_spec_ctrl, %edi
 	xor %edx, %edi
 	or %edi, %esi
-	ALTERNATIVE __stringify(je \label), "", X86_FEATURE_KERNEL_IBRS
+	je \label
 #endif
+999:
 	wrmsr
 .endm