Re: [edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib: Fix AP VolatileRegisters race condition

["Ni, Ray" <ray.ni@intel.com>]

Star,
You are right. There is no sequence requirement between FinishedCount++ and NumApsExecuting--.

In fact, I have submitted another bugzilla https://bugzilla.tianocore.org/show_bug.cgi?id=3179.
 
With that Bugzilla, the wait on (FinishedCount == CpuCount - 1) will be removed for the 1st wake up case.

Thanks,
Ray


> -----Original Message-----
> From: Zeng, Star <star.zeng@intel.com>
> Sent: Monday, January 25, 2021 4:43 PM
> To: Kinney, Michael D <michael.d.kinney@intel.com>; devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Laszlo
> Ersek <lersek@redhat.com>; Kumar, Rahul1 <rahul1.kumar@intel.com>;
> Zeng, Star <star.zeng@intel.com>
> Subject: RE: [edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib: Fix AP
> VolatileRegisters race condition
> 
> Mike,
> 
> Oh, see it.
> There is no sequence dependence between FinishedCount increment and
> NumApsExecuting decrement, right?
> 
>      InterlockedIncrement ((UINT32 *) &CpuMpData->FinishedCount);
> 
>      InterlockedDecrement ((UINT32 *) &CpuMpData->MpCpuExchangeInfo-
> >NumApsExecuting);
> 
> 
> Thanks,
> Star
> 
> > -----Original Message-----
> > From: Kinney, Michael D <michael.d.kinney@intel.com>
> > Sent: Monday, January 25, 2021 1:16 PM
> > To: Zeng, Star <star.zeng@intel.com>; devel@edk2.groups.io; Kinney,
> > Michael D <michael.d.kinney@intel.com>
> > Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Laszlo
> > Ersek <lersek@redhat.com>; Kumar, Rahul1 <rahul1.kumar@intel.com>
> > Subject: RE: [edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib: Fix AP
> > VolatileRegisters race condition
> >
> > Hi Star,
> >
> > That line is only active when (CpuMpData->SevEsIsEnabled) is TRUE.
> >
> > The race condition addressed by this BZ is for systems with SecEsIsEnabled
> > FALSE.
> >
> > From comments in this file the SecEsIsEnabled cases have already been
> > handled.
> >
> > Mike
> >
> > > -----Original Message-----
> > > From: Zeng, Star <star.zeng@intel.com>
> > > Sent: Sunday, January 24, 2021 7:15 PM
> > > To: devel@edk2.groups.io; Kinney, Michael D
> > > <michael.d.kinney@intel.com>
> > > Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>;
> > > Laszlo Ersek <lersek@redhat.com>; Kumar, Rahul1
> > > <rahul1.kumar@intel.com>; Zeng, Star <star.zeng@intel.com>
> > > Subject: RE: [edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib:
> > > Fix AP VolatileRegisters race condition
> > >
> > > Does
> > >
> >
> https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpIni
> > > tLib/MpLib.c#L909 (also decrements
> > > NumApsExecuting) also need be handled?
> > >
> > > Thanks,
> > > Star
> > >
> > > > -----Original Message-----
> > > > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of
> > > > Michael D Kinney
> > > > Sent: Saturday, January 23, 2021 1:10 AM
> > > > To: devel@edk2.groups.io
> > > > Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>;
> > > > Laszlo Ersek <lersek@redhat.com>; Kumar, Rahul1
> > > > <rahul1.kumar@intel.com>
> > > > Subject: [edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib: Fix
> > > > AP VolatileRegisters race condition
> > > >
> > > > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3182
> > > >
> > > > Fix the order of operations in ApWakeupFunction() when
> > > > PcdCpuApLoopMode is set to HLT mode that uses INIT-SIPI-SIPI to
> wake
> > > > APs.  In this mode, volatile state is restored and saved each time a
> > > > INIT-SIPI-SIPI is sent to an AP to request a function to be executed
> > > > on the AP.  When the function is completed the volatile state of the
> > > > AP is saved.  However, the counters NumApsExecuting and
> > > > FinishedCount are updated before the volatile state is saved.  This
> > > > allows for a race condition window for the BSP that is waiting on
> > > > these counters to request a new INIT-SIPI-SIPI before all the APs
> > > > have completely saved their volatile state.  The fix is to save the
> > > > AP volatile state before updating the NumApsExecuting and
> > > > FinishedCount counters.
> > > >
> > > > Cc: Eric Dong <eric.dong@intel.com>
> > > > Cc: Ray Ni <ray.ni@intel.com>
> > > > Cc: Laszlo Ersek <lersek@redhat.com>
> > > > Cc: Rahul Kumar <rahul1.kumar@intel.com>
> > > > Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
> > > > ---
> > > >  UefiCpuPkg/Library/MpInitLib/MpLib.c | 31
> > > > ++++++++++++++++------------
> > > >  1 file changed, 18 insertions(+), 13 deletions(-)
> > > >
> > > > diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > > b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > > index 681fa79b4cff..8b1f7f84bad6 100644
> > > > --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > > +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > > @@ -769,15 +769,6 @@ ApWakeupFunction (
> > > >        RestoreVolatileRegisters
> > > > (&CpuMpData->CpuData[0].VolatileRegisters,
> > > > FALSE);
> > > >        InitializeApData (CpuMpData, ProcessorNumber, BistData,
> > > > ApTopOfStack);
> > > >        ApStartupSignalBuffer = CpuMpData-
> > > > >CpuData[ProcessorNumber].StartupApSignal;
> > > > -
> > > > -      //
> > > > -      // Delay decrementing the APs executing count when SEV-ES is
> > enabled
> > > > -      // to allow the APs to issue an AP_RESET_HOLD before the BSP
> > possibly
> > > > -      // performs another INIT-SIPI-SIPI sequence.
> > > > -      //
> > > > -      if (!CpuMpData->SevEsIsEnabled) {
> > > > -        InterlockedDecrement ((UINT32 *) &CpuMpData-
> > > > >MpCpuExchangeInfo->NumApsExecuting);
> > > > -      }
> > > >      } else {
> > > >        //
> > > >        // Execute AP function if AP is ready @@ -866,19 +857,33 @@
> > > > ApWakeupFunction (
> > > >        }
> > > >      }
> > > >
> > > > +    if (CpuMpData->ApLoopMode == ApInHltLoop) {
> > > > +      //
> > > > +      // Save AP volatile registers
> > > > +      //
> > > > +      SaveVolatileRegisters (&CpuMpData-
> > > > >CpuData[ProcessorNumber].VolatileRegisters);
> > > > +    }
> > > > +
> > > >      //
> > > >      // AP finished executing C code
> > > >      //
> > > >      InterlockedIncrement ((UINT32 *) &CpuMpData->FinishedCount);
> > > >
> > > > +    if (CpuMpData->InitFlag == ApInitConfig) {
> > > > +      //
> > > > +      // Delay decrementing the APs executing count when SEV-ES is
> > enabled
> > > > +      // to allow the APs to issue an AP_RESET_HOLD before the BSP
> > possibly
> > > > +      // performs another INIT-SIPI-SIPI sequence.
> > > > +      //
> > > > +      if (!CpuMpData->SevEsIsEnabled) {
> > > > +        InterlockedDecrement ((UINT32 *) &CpuMpData-
> > > > >MpCpuExchangeInfo->NumApsExecuting);
> > > > +      }
> > > > +    }
> > > > +
> > > >      //
> > > >      // Place AP is specified loop mode
> > > >      //
> > > >      if (CpuMpData->ApLoopMode == ApInHltLoop) {
> > > > -      //
> > > > -      // Save AP volatile registers
> > > > -      //
> > > > -      SaveVolatileRegisters (&CpuMpData-
> > > > >CpuData[ProcessorNumber].VolatileRegisters);
> > > >        //
> > > >        // Place AP in HLT-loop
> > > >        //
> > > > --
> > > > 2.29.2.windows.2
> > > >
> > > >
> > > >
> > > > 
> > > >