[edk2-devel] [Patch 1/1] UefiCpuPkg/Library/MpInitLib: Fix AP VolatileRegisters race condition
Zeng, Star
star.zeng at intel.com
Mon Jan 25 03:14:43 UTC 2021
Does https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/MpInitLib/MpLib.c#L909 (also decrements NumApsExecuting) also need be handled?
Thanks,
Star
> -----Original Message-----
> From: devel at edk2.groups.io <devel at edk2.groups.io> On Behalf Of Michael
> D Kinney
> Sent: Saturday, January 23, 2021 1:10 AM
> To: devel at edk2.groups.io
> Cc: Dong, Eric <eric.dong at intel.com>; Ni, Ray <ray.ni at intel.com>; Laszlo
> Ersek <lersek at redhat.com>; Kumar, Rahul1 <rahul1.kumar at 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 at intel.com>
> Cc: Ray Ni <ray.ni at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Rahul Kumar <rahul1.kumar at intel.com>
> Signed-off-by: Michael D Kinney <michael.d.kinney at 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
>
>
>
>
>
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