Race condition between APHandler's release of Busy spinlock and
user-triggered SmmStartupThisAP's acquisition attempt of the Busy spinlock
(non-blocking mode).
UserProc is the user's procedure to execute on an AP.
UserProcCompletion is the user procedure's completion spinlock.
All other variables are from EDK2.
BSP AP
=====================================================================================
APHandler ()
WaitForSemaphore (Run)
<< initial
state >>
AcquireSpinLock (UserProcCompletion)
SmmStartupThisAp (Procedure)
AcquireSpinLockOrFail (Busy)
ReleaseSemaphore (Run)
UserProc ()
DoStuff() DoSomeOtherStuff ()
AcquireSpinLockOrFail (UserProcCompletion) AcquireSpinLockOrFail
(UserProcCompletion)
^^ waiting in a loop for user procedure's
completion == these fail
ReleaseSpinLock (UserProcCompletion) AcquireSpinLockOrFail
(UserProcCompletion)
^^ this succeeds
ReleaseSpinLock (UserProcCompletion)
<< return control to the caller and
reenter the flow >>>
AcquireSpinLock (UserProcCompletion)
SmmStartupThisAp (Procedure)
AcquireSpinLockOrFail (Busy)
^^ this wins the race with AP's
ReleaseSpinLock and fails;
ReleaseSpinLock (Busy)
return EFI_INVALID_PARAMETER;
To remedy, if AcquireSpinLockOrFail (of the Busy spinlock) fails, perform
regular AcquireSpinLock -- this eliminates the race condition.
Signed-off-by: Damian Nikodem <damian.niko...@intel.com>
Cc: Eric Dong <eric.d...@intel.com>
Cc: Ray Ni <ray...@intel.com>
Cc: Benjamin You <benjamin....@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Krzysztof Rusocki <krzysztof.ruso...@intel.com>
diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
index d8d2b6f444..206e196a76 100644
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
@@ -1239,8 +1239,16 @@ InternalSmmStartupThisAp (
AcquireSpinLock (mSmmMpSyncData->CpuData[CpuIndex].Busy);
} else {
if (!AcquireSpinLockOrFail (mSmmMpSyncData->CpuData[CpuIndex].Busy)) {
- DEBUG((DEBUG_ERROR, "Can't acquire mSmmMpSyncData->CpuData[%d].Busy\n",
CpuIndex));
- return EFI_NOT_READY;
+ DEBUG ((DEBUG_INFO, "BSP[%d] finds AP[%d] busy at proc 0x%llX (param
0x%llX), ",
+ mSmmMpSyncData->BspIndex,
+ CpuIndex,
+ *mSmmMpSyncData->CpuData[CpuIndex].Procedure,
+ (VOID*)mSmmMpSyncData->CpuData[CpuIndex].Parameter));
+ DEBUG ((DEBUG_INFO, "new proc 0x%llX (param 0x%llX). Waiting for the
previous AP procedure to complete...\n",
+ Procedure,
+ ProcArguments));
+
+ AcquireSpinLock (mSmmMpSyncData->CpuData[CpuIndex].Busy);
}
*Token = (MM_COMPLETION) CreateToken ();
--------------------------------------------------------------------
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