Re: [PATCH v2 0/3] Put AP into safe hlt-loop code on S3 path

[Paolo Bonzini <pbonzini@redhat.com>]

On 14/11/2016 11:39, Laszlo Ersek wrote:
> You've tried that:
> 
> https://www.mail-archive.com/edk2-devel@lists.01.org/msg02840.html
> https://www.mail-archive.com/edk2-devel@lists.01.org/msg02923.html

Uh, right. :)

> Do you suggest to make the LocalApicLib instances usable at runtime?
> For that I think we'll need to cover the LAPIC address range with a
> runtime-marked EfiMemoryMappedIO area. This can be done in
> "OvmfPkg/SmmControl2Dxe".
> 
> Also, we'll need a LocalApicLib instance that registers a callback for
> SetVirtualAddressMap() and converts the LAPIC base address pointer.
> 
> Currently BaseXApicX2ApicLib.c's GetLocalApicBaseAddress() function uses
> the MSR_IA32_APIC_BASE register if it's available -- based on CPUID --,
> and falls back to PcdCpuLocalApicBaseAddress otherwise. And only
> PcdCpuLocalApicBaseAddress is what we could replace with the virtual
> pointer. We can't accommodate a guest OS that reprograms the LAPIC base
> address.
> 
> Jeff, what do you think?
> 
> Anyway, I believe KVM doesn't support moving the LAPIC window; is that
> right?

No, it doesn't.  Let's add a backdoor in QEMU, where writing a given
value to port 0xb2 would start generating SMIs to all CPUs.  Then you
can write this somewhere in the initialization code, and in the S3 boot
script.

Paolo