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

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

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.

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

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(-)
>