Re: [PATCH Part2 RFC v4 01/40] KVM: SVM: Add support to handle AP reset MSR protocol

[Joerg Roedel]

On Wed, Jul 14, 2021 at 08:17:29PM +0000, Sean Christopherson wrote:
> On Wed, Jul 07, 2021, Brijesh Singh wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > 
> > Add support for AP Reset Hold being invoked using the GHCB MSR protocol,
> > available in version 2 of the GHCB specification.
> 
> Please provide a brief overview of the protocol, and why it's needed.  I assume
> it's to allow AP wakeup without a shared GHCB?

Yes, this is needed for SEV-ES kexec support to park APs without the
need for memory that will be owned by the new kernel when APs are woken
up.

You can have a look into my SEV-ES kexec/kdump patch-set for details:

	https://lore.kernel.org/lkml/20210705082443.14721-1-joro@xxxxxxxxxx/

I also sent this patch separatly earlier this week to enable GHCB
protocol version 2 support in KVM.

Regards,

	Joerg