On 01/29/21 01:59, 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 <ler...@redhat.com>
> Cc: Jordan Justen <jordan.l.jus...@intel.com>
> Cc: Ard Biesheuvel <ard.biesheu...@arm.com>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
> Cc: Aaron Young <aaron.yo...@oracle.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
> Signed-off-by: Ankur Arora <ankur.a.ar...@oracle.com>
> ---
> OvmfPkg/CpuHotplugSmm/CpuHotplug.c | 84
> ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 84 insertions(+)
>
> diff --git a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> index 05b1f8cb63a6..70d69f6ed65b 100644
> --- a/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> +++ b/OvmfPkg/CpuHotplugSmm/CpuHotplug.c
> @@ -188,6 +188,88 @@ 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().
> +
(1) Please drop this empty line (just before the '**/').
> +**/
> +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_INFO, "%a: did not find APIC ID " FMT_APIC_ID
> + " to unplug\n", __FUNCTION__, RemoveApicId));
(2) Please use DEBUG_VERBOSE here.
(I agree that we should have *one* DEBUG_INFO message that relates to
the removal of an individual processor; however, I think we should emit
that message when we finally signal QEMU to eject the processor.)
(3) Please un-indent ("outdent"?) the second line by two spaces.
> + ToUnplugIdx++;
> + continue;
> + }
> +
> + //
> + // Mark ProcessorNum for removal from SMM data structures
> + //
> + Status = mMmCpuService->RemoveProcessor (mMmCpuService, ProcessorNum);
> +
(4) It would be more idiomatic to remove this empty line (between Status
assignment and check).
> + if (EFI_ERROR (Status)) {
> + DEBUG ((DEBUG_ERROR, "%a: RemoveProcessor(" FMT_APIC_ID "): %r\n",
> + __FUNCTION__, RemoveApicId, Status));
> + goto Fatal;
(5) Please just "return Status" here, and drop the "Fatal" label.
> + }
> +
> + ToUnplugIdx++;
> + }
> +
> + //
> + // We've removed this set of APIC IDs from SMM data structures.
> + //
> + return EFI_SUCCESS;
> +
> +Fatal:
> + return Status;
> +}
> +
> +/**
> CPU Hotplug MMI handler function.
>
> This is a root MMI handler.
> @@ -303,6 +385,8 @@ CpuHotplugMmi (
>
> if (PluggedCount > 0) {
> Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
> + } else if (ToUnplugCount > 0) {
> + Status = UnplugCpus (mToUnplugApicIds, ToUnplugCount);
> }
>
> if (EFI_ERROR(Status)) {
>
(6) Hmm... What's the reason for the exclusivity?
Why is the following not better:
if (PluggedCount > 0) {
Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
if (EFI_ERROR (Status)) {
goto Fatal;
}
}
if (ToUnplugCount > 0) {
Status = UnplugCpus (mToUnplugApicIds, ToUnplugCount);
if (EFI_ERROR (Status)) {
goto Fatal;
}
}
QemuCpuhpCollectApicIds() intentionally populates both arrays in a
single go. As I suggested earlier:
https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg06711.html
msgid: <a92b50df-f693-ebda-e549-7bc9e6d2d...@redhat.com>
> [...] please handle plugs first, for which unused slots in
> mCpuHotPlugData.ApicId will be populated, and *then* handle removals
> (in the same invocation of CpuHotplugMmi()).
Did that turn out as unviable (the "same invocation of CpuHotplugMmi()"
part)?
(7) As a side note, addressing point (6) above would allow you to
address my point (13) from the v5 patch#1 thread, too; i.e., nesting the
Status check under (PluggedCount > 0).
Thanks!
Laszlo
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