Re: [PATCH v2 4/5] UefiCpuPkg/DxeMpLib: Fix bug when getting target C-State from eax

[Laszlo Ersek <lersek@redhat.com>]

On 11/25/16 07:03, Jeff Fan wrote:
> AP will get target C-State from eax[7:4]. We do shift in ebx firstly before set
> to eax. It will lead ebx is correct in the next time.

Please replace the word "correct" with "incorrect" in the commit message
-- without the patch, ebx is wrong at the second and further iterations.

With that word changed:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks!
Laszlo

> 
> The fix is to set ebx to eax firstly and does shift in eax. Thus, ebx could keep
> original value.
> 
> Reported-by: Laszlo Ersek <lersek@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Feng Tian <feng.tian@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Jeff Fan <jeff.fan@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
> index f8f4712..34c07a6 100644
> --- a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
> +++ b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
> @@ -266,8 +266,8 @@ MwaitLoop:
>      xor        ecx, ecx           ; ecx = 0
>      xor        edx, edx           ; edx = 0
>      monitor
> -    shl        ebx, 4
>      mov        eax, ebx           ; Mwait Cx, Target C-State per eax[7:4]
> +    shl        eax, 4
>      mwait
>      jmp        MwaitLoop
>  HltLoop:
>