Re: [edk2-devel] [PATCH v2 5/6] UefiCpuPkg/PiSmmCpuDxeSmm: Invert ReleaseAllAPs & InitializeDebugAgent

["Ni, Ray" <ray.ni@intel.com>]

Source level debugging in SMM doesn't enable timer interrupt so it does not support break-in from HOST debugger.
It only supports debugging AP code which is stopped by breakpoints.
I agree that with this change, the debug window of APs is a bit increased.

Reviewed-by: Ray Ni <ray.ni@intel.com>

Thanks,
Ray
> -----Original Message-----
> From: Wu, Jiaxin <jiaxin.wu@intel.com>
> Sent: Tuesday, December 26, 2023 12:21 AM
> To: devel@edk2.groups.io
> Cc: Laszlo Ersek <lersek@redhat.com>; Dong, Eric <eric.dong@intel.com>; Ni,
> Ray <ray.ni@intel.com>; Zeng, Star <star.zeng@intel.com>; Gerd Hoffmann
> <kraxel@redhat.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>
> Subject: [PATCH v2 5/6] UefiCpuPkg/PiSmmCpuDxeSmm: Invert
> ReleaseAllAPs & InitializeDebugAgent
> 
> Existing BSP handler stops source level debug, then call ReleaseAllAPs
> to tell all APs can reset the Present flag to FALSE:
>   InitializeDebugAgent (); /// Stop source level debug
>   ReleaseAllAPs ();        /// Tell APs can reset "Present" flag.
> 
> This patch is to invert ReleaseAllAPs & InitializeDebugAgent:
>   ReleaseAllAPs ();        /// Tell APs can reset "Present" flag.
>   InitializeDebugAgent (); /// Stop source level debug
> 
> After this change, there is no negative impact since SMM source level
> debug feature doesn't depend on AP's "Present" flag, no impact to the
> SMM source level debug capability.
> 
> Instead, the change will benefit the AP source level debug capability
> to trace its "Present" flag change for SMI exit since the source
> level debug feature will be stopped after each AP has the chance to
> reset the state.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Zeng Star <star.zeng@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> index bd2c9f841b..9aa9908863 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> @@ -648,23 +648,23 @@ BSPHandler (
>    //
>    // Wait for all APs to complete their pending tasks including MTRR
> programming if needed.
>    //
>    SmmCpuSyncWaitForAPs (mSmmMpSyncData->SyncContext, ApCount,
> CpuIndex);
> 
> +  //
> +  // Signal APs to Reset states/semaphore for this processor
> +  //
> +  ReleaseAllAPs ();
> +
>    if (mSmmDebugAgentSupport) {
>      //
>      // Stop source level debug in BSP handler, the code below will not be
>      // debugged.
>      //
>      InitializeDebugAgent (DEBUG_AGENT_INIT_EXIT_SMI, NULL, NULL);
>    }
> 
> -  //
> -  // Signal APs to Reset states/semaphore for this processor
> -  //
> -  ReleaseAllAPs ();
> -
>    //
>    // Perform pending operations for hot-plug
>    //
>    SmmCpuUpdate ();
> 
> --
> 2.16.2.windows.1



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