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

[Paolo Bonzini]

On 21/08/19 19:25, Kinney, Michael D wrote:
> Could we have an initial SMBASE that is within TSEG.
> 
> If we bring in hot plug CPUs one at a time, then initial
> SMBASE in TSEG can reprogram the SMBASE to the correct 
> value for that CPU.
> 
> Can we add a register to the hot plug controller that
> allows the BSP to set the initial SMBASE value for 
> a hot added CPU?  The default can be 3000:8000 for
> compatibility.
> 
> Another idea is when the SMI handler runs for a hot add
> CPU event, the SMM monarch programs the hot plug controller
> register with the SMBASE to use for the CPU that is being
> added.  As each CPU is added, a different SMBASE value can
> be programmed by the SMM Monarch.

Yes, all of these would work.  Again, I'm interested in having something
that has a hope of being implemented in real hardware.

Another, far easier to implement possibility could be a lockable MSR
(could be the existing MSR_SMM_FEATURE_CONTROL) that allows programming
the SMBASE outside SMM.  It would be nice if such a bit could be defined
by Intel.

Paolo