Re: [edk2-devel] [PATCH v1] UefiCpuPkg/MpInitLib: Fix possible uninitialized 'InitFlag' field

["Wu, Hao A" <hao.a.wu@intel.com>]

> -----Original Message-----
> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of
> Laszlo Ersek
> Sent: Friday, January 17, 2020 4:42 PM
> To: Wu, Hao A; devel@edk2.groups.io
> Cc: Dong, Eric; Ni, Ray; Kinney, Michael D
> Subject: Re: [edk2-devel] [PATCH v1] UefiCpuPkg/MpInitLib: Fix possible
> uninitialized 'InitFlag' field
> 
> 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.
> 

Sure.
I will update the commit message to add the information for such removal.

> 
> Also, it would be nice to reinstate the following comment:
> 
> //
> // Wait for all APs finish initialization
> //
> 
> just before the "while" statement.


Yes, I will add back this comment in the next version of patch.

Best Regards,
Hao Wu


> 
> Thanks
> Laszlo
> 
> 
>