Re: [PATCH v6 1/9] OvmfPkg/CpuHotplugSmm: refactor hotplug logic

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

On 01/29/21 01:59, Ankur Arora wrote:
> Refactor CpuHotplugMmi() to pull out the CPU hotplug logic into
> ProcessHotAddedCpus(). This is in preparation for supporting CPU
> hot-unplug.
> 
> 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:
>      > +  if (EFI_ERROR(Status)) {
>      > +    goto Fatal;
>      >    }
>     
>      (13) Without having seen the rest of the patches, I think this error
>      check should be nested under the same (PluggedCount > 0) condition; in
>      other words, I think it only makes sense to check Status after we
>      actually call ProcessHotAddedCpus().
>     
>     Addresses all comments from v5, except for this one, since the (lack) of
>     nesting makes more sense after patch 4, "OvmfPkg/CpuHotplugSmm: introduce
>     UnplugCpus()".
> 
>  OvmfPkg/CpuHotplugSmm/CpuHotplug.c | 214 ++++++++++++++++++++++---------------
>  1 file changed, 129 insertions(+), 85 deletions(-)

I've got one more trivial comment for this patch, to improve style
consistency with the rest of this driver:

> 
> diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> index cfe698ed2b5e..05b1f8cb63a6 100644
> --- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> +++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> @@ -62,6 +62,130 @@ STATIC UINT32 mPostSmmPenAddress;
>  //
>  STATIC EFI_HANDLE mDispatchHandle;
>  
> +/**
> +  Process CPUs that have been hot-added, per QemuCpuhpCollectApicIds().
> +
> +  For each such CPU, relocate the SMBASE, and report the CPU to PiSmmCpuDxeSmm
> +  via EFI_SMM_CPU_SERVICE_PROTOCOL. If the supposedly hot-added CPU is already
> +  known, skip it silently.
> +
> +  @param[in] PluggedApicIds    The APIC IDs of the CPUs that have been
> +                               hot-plugged.
> +
> +  @param[in] PluggedCount      The number of filled-in APIC IDs in
> +                               PluggedApicIds.
> +
> +  @retval EFI_SUCCESS          CPUs corresponding to all the APIC IDs are
> +                               populated.
> +
> +  @retval EFI_OUT_OF_RESOURCES Out of APIC ID space in "mCpuHotPlugData".
> +
> +  @return                      Error codes propagated from SmbaseRelocate()
> +                               and mMmCpuService->AddProcessor().
> +

(2) This empty line is not "wrong" in any case, just a bit inconsistent
with the rest of this driver; please drop it.

Thanks
Laszlo

> +**/
> +STATIC
> +EFI_STATUS
> +ProcessHotAddedCpus (
> +  IN APIC_ID                      *PluggedApicIds,
> +  IN UINT32                       PluggedCount
> +  )
> +{
> +  EFI_STATUS Status;
> +  UINT32     PluggedIdx;
> +  UINT32     NewSlot;
> +
> +  //
> +  // The Post-SMM Pen need not be reinstalled multiple times within a single
> +  // root MMI handling. Even reinstalling once per root MMI is only prudence;
> +  // in theory installing the pen in the driver's entry point function should
> +  // suffice.
> +  //
> +  SmbaseReinstallPostSmmPen (mPostSmmPenAddress);
> +
> +  PluggedIdx = 0;
> +  NewSlot = 0;
> +  while (PluggedIdx < PluggedCount) {
> +    APIC_ID NewApicId;
> +    UINT32  CheckSlot;
> +    UINTN   NewProcessorNumberByProtocol;
> +
> +    NewApicId = PluggedApicIds[PluggedIdx];
> +
> +    //
> +    // Check if the supposedly hot-added CPU is already known to us.
> +    //
> +    for (CheckSlot = 0;
> +         CheckSlot < mCpuHotPlugData->ArrayLength;
> +         CheckSlot++) {
> +      if (mCpuHotPlugData->ApicId[CheckSlot] == NewApicId) {
> +        break;
> +      }
> +    }
> +    if (CheckSlot < mCpuHotPlugData->ArrayLength) {
> +      DEBUG ((DEBUG_VERBOSE, "%a: APIC ID " FMT_APIC_ID " was hot-plugged "
> +        "before; ignoring it\n", __FUNCTION__, NewApicId));
> +      PluggedIdx++;
> +      continue;
> +    }
> +
> +    //
> +    // Find the first empty slot in CPU_HOT_PLUG_DATA.
> +    //
> +    while (NewSlot < mCpuHotPlugData->ArrayLength &&
> +           mCpuHotPlugData->ApicId[NewSlot] != MAX_UINT64) {
> +      NewSlot++;
> +    }
> +    if (NewSlot == mCpuHotPlugData->ArrayLength) {
> +      DEBUG ((DEBUG_ERROR, "%a: no room for APIC ID " FMT_APIC_ID "\n",
> +        __FUNCTION__, NewApicId));
> +      return EFI_OUT_OF_RESOURCES;
> +    }
> +
> +    //
> +    // Store the APIC ID of the new processor to the slot.
> +    //
> +    mCpuHotPlugData->ApicId[NewSlot] = NewApicId;
> +
> +    //
> +    // Relocate the SMBASE of the new CPU.
> +    //
> +    Status = SmbaseRelocate (NewApicId, mCpuHotPlugData->SmBase[NewSlot],
> +               mPostSmmPenAddress);
> +    if (EFI_ERROR (Status)) {
> +      goto RevokeNewSlot;
> +    }
> +
> +    //
> +    // Add the new CPU with EFI_SMM_CPU_SERVICE_PROTOCOL.
> +    //
> +    Status = mMmCpuService->AddProcessor (mMmCpuService, NewApicId,
> +                              &NewProcessorNumberByProtocol);
> +    if (EFI_ERROR (Status)) {
> +      DEBUG ((DEBUG_ERROR, "%a: AddProcessor(" FMT_APIC_ID "): %r\n",
> +        __FUNCTION__, NewApicId, Status));
> +      goto RevokeNewSlot;
> +    }
> +
> +    DEBUG ((DEBUG_INFO, "%a: hot-added APIC ID " FMT_APIC_ID ", SMBASE 0x%Lx, "
> +      "EFI_SMM_CPU_SERVICE_PROTOCOL assigned number %Lu\n", __FUNCTION__,
> +      NewApicId, (UINT64)mCpuHotPlugData->SmBase[NewSlot],
> +      (UINT64)NewProcessorNumberByProtocol));
> +
> +    NewSlot++;
> +    PluggedIdx++;
> +  }
> +
> +  //
> +  // We've processed this batch of hot-added CPUs.
> +  //
> +  return EFI_SUCCESS;
> +
> +RevokeNewSlot:
> +  mCpuHotPlugData->ApicId[NewSlot] = MAX_UINT64;
> +
> +  return Status;
> +}
>  
>  /**
>    CPU Hotplug MMI handler function.
> @@ -122,8 +246,6 @@ CpuHotplugMmi (
>    UINT8      ApmControl;
>    UINT32     PluggedCount;
>    UINT32     ToUnplugCount;
> -  UINT32     PluggedIdx;
> -  UINT32     NewSlot;
>  
>    //
>    // Assert that we are entering this function due to our root MMI handler
> @@ -179,87 +301,12 @@ CpuHotplugMmi (
>      goto Fatal;
>    }
>  
> -  //
> -  // Process hot-added CPUs.
> -  //
> -  // The Post-SMM Pen need not be reinstalled multiple times within a single
> -  // root MMI handling. Even reinstalling once per root MMI is only prudence;
> -  // in theory installing the pen in the driver's entry point function should
> -  // suffice.
> -  //
> -  SmbaseReinstallPostSmmPen (mPostSmmPenAddress);
> +  if (PluggedCount > 0) {
> +    Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
> +  }
>  
> -  PluggedIdx = 0;
> -  NewSlot = 0;
> -  while (PluggedIdx < PluggedCount) {
> -    APIC_ID NewApicId;
> -    UINT32  CheckSlot;
> -    UINTN   NewProcessorNumberByProtocol;
> -
> -    NewApicId = mPluggedApicIds[PluggedIdx];
> -
> -    //
> -    // Check if the supposedly hot-added CPU is already known to us.
> -    //
> -    for (CheckSlot = 0;
> -         CheckSlot < mCpuHotPlugData->ArrayLength;
> -         CheckSlot++) {
> -      if (mCpuHotPlugData->ApicId[CheckSlot] == NewApicId) {
> -        break;
> -      }
> -    }
> -    if (CheckSlot < mCpuHotPlugData->ArrayLength) {
> -      DEBUG ((DEBUG_VERBOSE, "%a: APIC ID " FMT_APIC_ID " was hot-plugged "
> -        "before; ignoring it\n", __FUNCTION__, NewApicId));
> -      PluggedIdx++;
> -      continue;
> -    }
> -
> -    //
> -    // Find the first empty slot in CPU_HOT_PLUG_DATA.
> -    //
> -    while (NewSlot < mCpuHotPlugData->ArrayLength &&
> -           mCpuHotPlugData->ApicId[NewSlot] != MAX_UINT64) {
> -      NewSlot++;
> -    }
> -    if (NewSlot == mCpuHotPlugData->ArrayLength) {
> -      DEBUG ((DEBUG_ERROR, "%a: no room for APIC ID " FMT_APIC_ID "\n",
> -        __FUNCTION__, NewApicId));
> -      goto Fatal;
> -    }
> -
> -    //
> -    // Store the APIC ID of the new processor to the slot.
> -    //
> -    mCpuHotPlugData->ApicId[NewSlot] = NewApicId;
> -
> -    //
> -    // Relocate the SMBASE of the new CPU.
> -    //
> -    Status = SmbaseRelocate (NewApicId, mCpuHotPlugData->SmBase[NewSlot],
> -               mPostSmmPenAddress);
> -    if (EFI_ERROR (Status)) {
> -      goto RevokeNewSlot;
> -    }
> -
> -    //
> -    // Add the new CPU with EFI_SMM_CPU_SERVICE_PROTOCOL.
> -    //
> -    Status = mMmCpuService->AddProcessor (mMmCpuService, NewApicId,
> -                              &NewProcessorNumberByProtocol);
> -    if (EFI_ERROR (Status)) {
> -      DEBUG ((DEBUG_ERROR, "%a: AddProcessor(" FMT_APIC_ID "): %r\n",
> -        __FUNCTION__, NewApicId, Status));
> -      goto RevokeNewSlot;
> -    }
> -
> -    DEBUG ((DEBUG_INFO, "%a: hot-added APIC ID " FMT_APIC_ID ", SMBASE 0x%Lx, "
> -      "EFI_SMM_CPU_SERVICE_PROTOCOL assigned number %Lu\n", __FUNCTION__,
> -      NewApicId, (UINT64)mCpuHotPlugData->SmBase[NewSlot],
> -      (UINT64)NewProcessorNumberByProtocol));
> -
> -    NewSlot++;
> -    PluggedIdx++;
> +  if (EFI_ERROR(Status)) {
> +    goto Fatal;
>    }
>  
>    //
> @@ -267,9 +314,6 @@ CpuHotplugMmi (
>    //
>    return EFI_SUCCESS;
>  
> -RevokeNewSlot:
> -  mCpuHotPlugData->ApicId[NewSlot] = MAX_UINT64;
> -
>  Fatal:
>    ASSERT (FALSE);
>    CpuDeadLoop ();
>