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

["Zeng, Star" <star.zeng@intel.com>]

BTW:

Do you think it worth or not to add the check like below in Edk2\UefiCpuPkg\Library\MpInitLib\PeiMpLib.c GetCpuMpData()? If the assert was there, it would facilitate the debug?

    CpuMpData = (CPU_MP_DATA *) (Idtr.Base + Idtr.Limit + 1);
+    ASSERT (CpuMpData != NULL);

Thanks,
Star
> -----Original Message-----
> From: Ni, Ray <ray.ni@intel.com>
> Sent: Monday, January 25, 2021 4:53 PM
> To: Zeng, Star <star.zeng@intel.com>; Kinney, Michael D
> <michael.d.kinney@intel.com>; devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@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
> 
> 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
> > > > >
> > > > >
> > > > >
> > > > > 
> > > > >