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

[Paolo Bonzini]

On 21/08/19 22:17, Kinney, Michael D wrote:
> Paolo,
> 
> It makes sense to match real HW.

Note that it'd also be fine to match some kind of official Intel
specification even if no processor (currently?) supports it.

> That puts us back to
> the reset vector and handling the initial SMI at
> 3000:8000.  That is all workable from a FW implementation
> perspective.  It look like the only issue left is DMA.
> 
> DMA protection of memory ranges is a chipset feature.
> For the current QEMU implementation, what ranges of
> memory are guaranteed to be protected from DMA?  Is
> it only A/B seg and TSEG?

Yes.

Paolo

>> 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