Re: [edk2-devel] [PATCH] UefiCpuPkg: Remove ASSERT checking if FinishedCount equal to CpuCount-1

["Yuanhao Xie" <yuanhao.xie@intel.com>]

Hi Laszlo,

Thanks a lot for the feedbacks and quick response.

I updated the commit message, please check v3.
The changes includes:
-An explanation for the first chunk, which aims to report the incrementation of "finished" for as late as possible.
-Renamed the subject line and added the module.
-Added "Fixes: 964a4f032dcd" to the commit message.

Regards
Yuanhao
-----Original Message-----
From: Laszlo Ersek <lersek@redhat.com> 
Sent: Wednesday, October 25, 2023 6:37 PM
To: devel@edk2.groups.io; Xie, Yuanhao <yuanhao.xie@intel.com>
Cc: Ni, Ray <ray.ni@intel.com>; Dong, Eric <eric.dong@intel.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>; Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [edk2-devel] [PATCH] UefiCpuPkg: Remove ASSERT checking if FinishedCount equal to CpuCount-1

On 10/25/23 12:07, Yuanhao Xie wrote:
> The purpose is to fix an assertion with applying the following patch
> series:
> 
> UefiCpuPkg: Refactor the logic for placing APs in HltLoop.
> UefiCpuPkg: Refactor the logic for placing APs in Mwait/Runloop.
> UefiCpuPkg: Create MpHandOff.
> UefiCpuPkg: ApWakeupFunction directly use CpuMpData.
> UefiCpuPkg: Eliminate the second INIT-SIPI-SIPI sequence.
> UefiCpuPkg: Decouple the SEV-ES functionality.
> 
> The assertion arises from a timing discrepancy between BSP completing 
> its startup signal check and the APs incrementing the FinishedCount.
> 
> Instead of assertion, use while loop to waits until all the APs have 
> incremented the FinishedCount.
> 
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Yuanhao Xie <yuanhao.xie@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c 
> b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index 6f1456cfe1..9a6ec5db5c 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -913,8 +913,8 @@ DxeApEntryPoint (
>    UINTN  ProcessorNumber;
>  
>    GetProcessorNumber (CpuMpData, &ProcessorNumber);
> -  InterlockedIncrement ((UINT32 *)&CpuMpData->FinishedCount);
>    RestoreVolatileRegisters (&CpuMpData->CpuData[0].VolatileRegisters, 
> FALSE);
> +  InterlockedIncrement ((UINT32 *)&CpuMpData->FinishedCount);
>    PlaceAPInMwaitLoopOrRunLoop (
>      CpuMpData->ApLoopMode,
>      CpuMpData->CpuData[ProcessorNumber].StartupApSignal,
> @@ -2201,7 +2201,12 @@ MpInitLibInitialize (
>        // looping process there.
>        //
>        SwitchApContext (MpHandOff);
> -      ASSERT (CpuMpData->FinishedCount == (CpuMpData->CpuCount - 1));
> +      //
> +      // Wait for all APs finished initialization
> +      //
> +      while (CpuMpData->FinishedCount < (CpuMpData->CpuCount - 1)) {
> +        CpuPause ();
> +      }
>  
>        //
>        // Set Apstate as Idle, otherwise Aps cannot be waken-up again.

The second hunk makes sense. SwitchApContext() returns after all APs are "live", but that doesn't guarantee that all APs are also "done" by the time the BSP reaches the FinishedCount check.

(1) What is the justification for the first hunk? I understand that we may want to report "finished" from an AP as late as possible. Is that the only (general) reason for the first hunk, or is there a specific reason?

Either way, the reason for the first hunk should be documented in the commit message.

(2) The subject line should be

  UefiCpuPkg/MpInitLib: wait for all APs to finish initialization

because

- we should also state the component name within UefiCpuPkg,

- "remove assert" is just a natural language expression of the direct code change, so it's not useful; what's useful is naming the *goal* that we're achieving.

(3) I suggest appending

  Fixes: 964a4f032dcd

to the commit message, just above your Signed-off-by.

Laszlo



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