[edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF

[Laszlo Ersek]

On 08/21/19 17:48, Kinney, Michael D wrote:
> Perhaps there is a way to avoid the 3000:8000 startup
> vector.
>
> If a CPU is added after a cold reset, it is already in a
> different state because one of the active CPUs needs to
> release it by interacting with the hot plug controller.
>
> Can the SMRR for CPUs in that state be pre-programmed to
> match the SMRR in the rest of the active CPUs?
>
> For OVMF we expect all the active CPUs to use the same
> SMRR value, so a check can be made to verify that all
> the active CPUs have the same SMRR value.  If they do,
> then any CPU released through the hot plug controller
> can have its SMRR pre-programmed and the initial SMI
> will start within TSEG.

Yes, that is what I proposed here:

* http://mid.mail-archive.com/effa5e32-be1e-4703-4419-8866b7754e2d@redhat.com
* https://edk2.groups.io/g/devel/message/45570

Namely:

> When the SMM setup quiesces during normal firmware boot, OVMF could
> use existent (finalized) SMBASE infomation to *pre-program* some
> virtual QEMU hardware, with such state that would be expected, as
> "final" state, of any new hotplugged CPU. Afterwards, if / when the
> hotplug actually happens, QEMU could blanket-apply this state to the
> new CPU, and broadcast a hardware SMI to all CPUs except the new one.

(I know that Paolo didn't like it; I'm just confirming that I had the
same, or at least a very similar, idea.)

Thanks!
Laszlo

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