Re: [PATCH v1] UefiCpuPkg/MpInitLib: Fix possible uninitialized 'InitFlag' field

["Laszlo Ersek" <lersek@redhat.com>]

On 01/17/20 07:56, Hao A Wu wrote:
> REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2474
> 
> Previous commit d786a17232:
> UefiCpuPkg/MpInitLib: Reduce the size when loading microcode patches
> 
> Removed the below assignments for the 'InitFlag' field of CPU_MP_DATA
> structure in function MpInitLibInitialize() when APs are waken up to do
> some initialize sync:
> 
> CpuMpData->InitFlag  = ApInitReconfig;
> ...
> CpuMpData->InitFlag = ApInitDone;
> 
> Under some cases (e.g. when variable OldCpuMpData is not NULL, which means
> function CollectProcessorCount() will not be called), this will left the
> 'InitFlag' field being uninitialized with a value of 0, which is a invalid
> value for the type of 'InitFlag' (AP_INIT_STATE).
> 
> It may potentially cause the WakeUpAP() function to run some unnecessary
> codes when the APs have been successfully waken up before:
> 
>   if (CpuMpData->WakeUpByInitSipiSipi ||
>       CpuMpData->InitFlag   != ApInitDone) {
>     ResetVectorRequired = TRUE;
>     AllocateResetVector (CpuMpData);
>     FillExchangeInfoData (CpuMpData);
>     SaveLocalApicTimerSetting (CpuMpData);
>   }
> 
> This commit will address the above-mentioned issue.
> 
> Test done:
> * OS boot on a real platform with multi processors
> 
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Signed-off-by: Hao A Wu <hao.a.wu@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index 6ec9b172b8..17e19395f2 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -1775,11 +1775,12 @@ MpInitLibInitialize (
>    // Wakeup APs to do some AP initialize sync (Microcode & MTRR)
>    //
>    if (CpuMpData->CpuCount > 1) {
> +    CpuMpData->InitFlag = ApInitReconfig;
>      WakeUpAP (CpuMpData, TRUE, 0, ApInitializeSync, CpuMpData, TRUE);
>      while (CpuMpData->FinishedCount < (CpuMpData->CpuCount - 1)) {
>        CpuPause ();
>      }
> -
> +    CpuMpData->InitFlag = ApInitDone;
>      for (Index = 0; Index < CpuMpData->CpuCount; Index++) {
>        SetApState (&CpuMpData->CpuData[Index], CpuStateIdle);
>      }
> 

It looks reasonable to me, but I was away while patch

"UefiCpuPkg/MpInitLib: Reduce the size when loading microcode patches"

was being reviewed, so I can't really say.

Can you explain (in the commit message) *why* commit d786a17232 removed
these InitFlag assignments? I've now read the commit message on
d786a17232, and it's not obvious to me.


Also, it would be nice to reinstate the following comment:

//
// Wait for all APs finish initialization
//

just before the "while" statement.

Thanks
Laszlo