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

[Paolo Bonzini]

On 4/8/26 20:22, Paolo Bonzini wrote:
> Reuse the same assembly as SVM, just with alternatives instead
> of cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS).
>
> Due to the dearth of registers in 32-bit x86, save/restore %eax
> across the restoring sequence, keeping it simple; the main alternative
> would be to leave vmx and flags on the stack, avoiding the need to read
> flags from %ebx.  It's not really measurable difference.
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   arch/x86/kvm/vmenter.h     |  4 ++--
>   arch/x86/kvm/vmx/vmenter.S | 25 +++++++++++++++----------
>   arch/x86/kvm/vmx/vmx.c     | 25 -------------------------
>   arch/x86/kvm/vmx/vmx.h     |  1 -
>   4 files changed, 17 insertions(+), 38 deletions(-)
>
> diff --git a/arch/x86/kvm/vmenter.h b/arch/x86/kvm/vmenter.h
> index e746e1328d3f..d822dafc75f7 100644
> --- a/arch/x86/kvm/vmenter.h
> +++ b/arch/x86/kvm/vmenter.h
> @@ -55,7 +55,7 @@
>   #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

>   	movl %edx, %eax
>   	shr $32, %rdx
>   #else
> @@ -66,7 +66,7 @@
>   	mov 4 + \guest_spec_ctrl, %edi
>   	xor %edx, %edi
>   	or %edi, %esi
> -	je \label
> +	ALTERNATIVE "", __stringify(je \label), X86_FEATURE_KERNEL_IBRS

Same here.

Paolo