Re: [edk2-devel] [PATCH v8 04/10] OvmfPkg/CpuHotplugSmm: introduce UnplugCpus()

["Laszlo Ersek" <lersek@redhat.com>]

On 02/22/21 08:19, Ankur Arora wrote:
> Introduce UnplugCpus() which maps each APIC ID being unplugged
> onto the hardware ID of the processor and informs PiSmmCpuDxeSmm
> of removal by calling EFI_SMM_CPU_SERVICE_PROTOCOL.RemoveProcessor().
> 
> With this change we handle the first phase of unplug where we collect
> the CPUs that need to be unplugged and mark them for removal in SMM
> data structures.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Aaron Young <aaron.young@oracle.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
> 
> Notes:
>     Addresses these review comments from v6:
>      (1) Drop the empty line in the comment block around UnplugCpus().
>      (2) Make the "did not find APIC ID" DEBUG_VERBOSE instead of DEBUG_INFO.
>      (3) Un-Indented ("Outdented") the line following the comment "Ignore the
>       unplug if APIC ID.
>      (4) Remove the empty line between Status assignment and check.
>      (5) Drop the "goto Fatal" logic and just return Status directly.
>      (6) Handle both Plugging and Unplugging of CPUs in one go.
>      (7) Also nest the EFI_STATUS check.
> 
>  OvmfPkg/CpuHotplugSmm/CpuHotplug.c | 84 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 84 insertions(+)
> 
> diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> index 3192bfea1f15..f07b5072749a 100644
> --- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> +++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> @@ -188,6 +188,83 @@ RevokeNewSlot:
>  }
>  
>  /**
> +  Process to be hot-unplugged CPUs, per QemuCpuhpCollectApicIds().
> +
> +  For each such CPU, report the CPU to PiSmmCpuDxeSmm via
> +  EFI_SMM_CPU_SERVICE_PROTOCOL. If the to be hot-unplugged CPU is
> +  unknown, skip it silently.
> +
> +  @param[in] ToUnplugApicIds    The APIC IDs of the CPUs that are about to be
> +                                hot-unplugged.
> +
> +  @param[in] ToUnplugCount      The number of filled-in APIC IDs in
> +                                ToUnplugApicIds.
> +
> +  @retval EFI_SUCCESS           Known APIC IDs have been removed from SMM data
> +                                structures.
> +
> +  @return                       Error codes propagated from
> +                                mMmCpuService->RemoveProcessor().
> +**/
> +STATIC
> +EFI_STATUS
> +UnplugCpus (
> +  IN APIC_ID                      *ToUnplugApicIds,
> +  IN UINT32                       ToUnplugCount
> +  )
> +{
> +  EFI_STATUS Status;
> +  UINT32     ToUnplugIdx;
> +  UINTN      ProcessorNum;
> +
> +  ToUnplugIdx = 0;
> +  while (ToUnplugIdx < ToUnplugCount) {
> +    APIC_ID    RemoveApicId;
> +
> +    RemoveApicId = ToUnplugApicIds[ToUnplugIdx];
> +
> +    //
> +    // mCpuHotPlugData->ApicId maps ProcessorNum -> ApicId. Use it to find
> +    // the ProcessorNum for the APIC ID to be removed.
> +    //
> +    for (ProcessorNum = 0;
> +         ProcessorNum < mCpuHotPlugData->ArrayLength;
> +         ProcessorNum++) {
> +      if (mCpuHotPlugData->ApicId[ProcessorNum] == RemoveApicId) {
> +        break;
> +      }
> +    }
> +
> +    //
> +    // Ignore the unplug if APIC ID not found
> +    //
> +    if (ProcessorNum == mCpuHotPlugData->ArrayLength) {
> +      DEBUG ((DEBUG_VERBOSE, "%a: did not find APIC ID " FMT_APIC_ID
> +        " to unplug\n", __FUNCTION__, RemoveApicId));
> +      ToUnplugIdx++;
> +      continue;
> +    }
> +
> +    //
> +    // Mark ProcessorNum for removal from SMM data structures
> +    //
> +    Status = mMmCpuService->RemoveProcessor (mMmCpuService, ProcessorNum);
> +    if (EFI_ERROR (Status)) {
> +      DEBUG ((DEBUG_ERROR, "%a: RemoveProcessor(" FMT_APIC_ID "): %r\n",
> +        __FUNCTION__, RemoveApicId, Status));
> +      return Status;
> +    }
> +
> +    ToUnplugIdx++;
> +  }
> +
> +  //
> +  // We've removed this set of APIC IDs from SMM data structures.
> +  //
> +  return EFI_SUCCESS;
> +}
> +
> +/**
>    CPU Hotplug MMI handler function.
>  
>    This is a root MMI handler.
> @@ -309,6 +386,13 @@ CpuHotplugMmi (
>      }
>    }
>  
> +  if (ToUnplugCount > 0) {
> +    Status = UnplugCpus (mToUnplugApicIds, ToUnplugCount);
> +    if (EFI_ERROR (Status)) {
> +      goto Fatal;
> +    }
> +  }
> +
>    //
>    // We've handled this MMI.
>    //
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>