Re: [edk2-devel] [RFC PATCH 0/5] support CPU hot-unplug

["Ankur Arora" <ankur.a.arora@oracle.com>]

On 2020-12-21 6:44 a.m., Laszlo Ersek wrote:
> Hi Ankur,
> 
> On 12/08/20 06:34, Ankur Arora wrote:
>> [ Resending to the correct edk2 alias this time. ]
>>
>> Hi,
>>
>> This series adds support for CPU hot-unplug with OVMF.
>>
>> Please see this in conjunction with the QEMU v2 series posted here:
>>    https://lore.kernel.org/qemu-devel/20201207140739.3829993-1-imammedo@redhat.com/
>>
>> In particular, would be glad for comments on Patch 4, specifically
>> where we should be ejecting the CPU.
>>
>> Right now the ejection happens in UnplugCpus() (called from
>> CpuHotplugMmi()):
>>    +    QemuCpuhpWriteCpuSelector (mMmCpuIo, RemoveApicId);
>>    +    QemuCpuhpWriteCpuStatus (mMmCpuIo, QEMU_CPUHP_STAT_EJECTED);
>>
>> That is way too early -- given that the actual unplug will happen
>> in SmmCpuUpdate() and given that the BSPHandler() would have waited
>> for the APs multiple times before then.
>>
>> Another possibility is that the actual ejection be deferred to the
>> _EJ0 method after the return from the SMI. But, that seems like a
>> hack. Additionally, Igor points out here that this approach has problems:
>>    https://lore.kernel.org/qemu-devel/20201204170939.1815522-1-imammedo@redhat.com/
> 
> I've filed:
> 
>    https://bugzilla.tianocore.org/show_bug.cgi?id=3132
> 
> Can you please register an account in the TianoCore Bugzilla at
> <https://bugzilla.tianocore.org/>, and assign the above ticket to yourself?
> 
> And then, the URL of the new BZ ticket should be included in every
> commit message, like this:
> 
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
> 
> just above your S-o-b.

Sure. Will do.
  
> No need to repost just because of this; I'll review the RFC series later.

Actually could you hold off before reviewing the RFC series. I'll be sending
a v2 series shortly. That does the actual unplug via SmmCpuFeaturesRendezvousExit()
(I had described the approach elsewhere in this thread.)

Thanks
Ankur

> Thanks,
> Laszlo
> 
>>
>> Please review.
>>
>> Thanks
>> Ankur
>>
>> Ankur Arora (5):
>>    OvmfPkg/CpuHotplugSmm: move CPU Hotplug into PlugCpus()
>>    OvmfPkg/CpuHotplugSmm: handle fw_remove
>>    OvmfPkg/CpuHotplugSmm: add CpuStatus helper function
>>    OvmfPkg/CpuHotplugSmm: handle CPU hot-unplug
>>    OvmfPkg/SmmControl2Dxe: negotiate ICH9_LPC_SMI_F_CPU_HOT_UNPLUG
>>
>>   OvmfPkg/CpuHotplugSmm/CpuHotplug.c            | 293 ++++++++++++------
>>   OvmfPkg/CpuHotplugSmm/QemuCpuhp.c             |  58 +++-
>>   OvmfPkg/CpuHotplugSmm/QemuCpuhp.h             |   6 +
>>   .../Include/IndustryStandard/QemuCpuHotplug.h |   2 +
>>   OvmfPkg/SmmControl2Dxe/SmiFeatures.c          |  21 +-
>>   5 files changed, 280 insertions(+), 100 deletions(-)
>>
>