Re: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: Clear some semaphores on S3 boot path

["Fan, Jeff" <jeff.fan@intel.com>]

Laszlo,

Thanks your comments. I added my comments as below in [Jeff]

Thanks!
Jeff

-----Original Message-----
From: Laszlo Ersek [mailto:lersek@redhat.com] 
Sent: Wednesday, November 30, 2016 4:49 AM
To: Fan, Jeff; edk2-devel@ml01.01.org
Cc: Kinney, Michael D; Yao, Jiewen; Tian, Feng
Subject: Re: [edk2] [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: Clear some semaphores on S3 boot path

On 11/29/16 08:51, Jeff Fan wrote:
> Some semaphores are not cleared on S3 boot path. For example,
> mSmmMpSyncData->CpuData[CpuIndex].Present. It may still keeps the 
> mSmmMpSyncData->value set at
> SMM runtime during S3 resume. It may causes BSP have the wrong 
> judgement on SMM AP's present state.
> 
> We have one related fix at e78a2a49ee6b0c0d7c6997c87ace31d7761cf636. 
> But that is not completed.
> 
> This fix is to clear Busy/Run/Present semaphores in InitializeMpSyncData().
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Feng Tian <feng.tian@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Jeff Fan <jeff.fan@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c 
> b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> index cfbf59e..a873b68 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> @@ -1357,6 +1357,9 @@ InitializeMpSyncData (
>          (UINT32 *)((UINTN)mSmmCpuSemaphores.SemaphoreCpu.Run + mSemaphoreSize * CpuIndex);
>        mSmmMpSyncData->CpuData[CpuIndex].Present =
>          (BOOLEAN *)((UINTN)mSmmCpuSemaphores.SemaphoreCpu.Present + 
> mSemaphoreSize * CpuIndex);
> +      *(mSmmMpSyncData->CpuData[CpuIndex].Busy)    = 0;
> +      *(mSmmMpSyncData->CpuData[CpuIndex].Run)     = 0;
> +      *(mSmmMpSyncData->CpuData[CpuIndex].Present) = FALSE;
>      }
>    }
>  }
> 

Even after this patch, the values pointed-to by the following fields of SemaphoreGlobal are not cleared: PFLock, CodeAccessCheckLock, MemoryMappedLock. Is that okay?

The values pointed-to by the following fields of SemaphoreMsr are not cleared either: Msr, AvailableCounter. Is that okay?

[Jeff] We need to clear the data in SMM_CPU_DATA_BLOCK/SMM_DISPATCHER_MP_SYNC_DATA and semaphores pointed by the field in those 2 structures.  However, the other spinlock located in SemaphoreBlock needn't to be cleared.

Can we imitate e78a2a49ee6b0c0d7c6997c87ace31d7761cf636 here; namely, can we save "SemaphoreBlock" and "TotalSize" from
InitializeSmmCpuSemaphores() in global variables (in SMRAM), and then just do another ZeroMem() here? That would cover the currently listed objects (*Counter, *InsideSmm, *AllCpusInSync), and everything else too, in a future-proof way.

[Jeff] This issue is that ZeroMem only clear all the fields in structure and needn't o clear the buffer pointed by these fields.

In fact, I wonder if the ZeroMem() could be moved into
InitializeMpSyncData() from InitializeSmmCpuSemaphores().

 [Jeff] If we cleared all semaphores(including Spinlock), we need to re-initialize them again. I do not think there is some reasonable usage case to let spinlock keep the garbage value.

Of course, if some pointed-to objects must not be cleared, then the
ZeroMem() is not appropriate.

[Jeff]  Agree.

Thanks!
Laszlo