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Message-ID: <fc32a469ae219763f80ef1fc9f151a62cfe76ed6.camel@linux.ibm.com>
Subject: Re: [RFC v2] KVM: x86: Support KVM VMs sharing SEV context
From:   James Bottomley <jejb@linux.ibm.com>
Reply-To: jejb@linux.ibm.com
To:     Steve Rutherford <srutherford@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Ashish Kalra <ashish.kalra@amd.com>,
        Nathan Tempelman <natet@google.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        X86 ML <x86@kernel.org>, KVM list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        David Rientjes <rientjes@google.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        dovmurik@linux.vnet.ibm.com, lersek@redhat.com, frankeh@us.ibm.com
Date:   Thu, 08 Apr 2021 14:15:41 -0700
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References: <20210316014027.3116119-1-natet@google.com>
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         <87bdd3a6-f5eb-91e4-9442-97dfef231640@redhat.com>
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On Thu, 2021-04-08 at 12:48 -0700, Steve Rutherford wrote:
> On Thu, Apr 8, 2021 at 10:43 AM James Bottomley <jejb@linux.ibm.com>
> wrote:
> > On Fri, 2021-04-02 at 16:20 +0200, Paolo Bonzini wrote:
> > > On 02/04/21 13:58, Ashish Kalra wrote:
> > > > Hi Nathan,
> > > > 
> > > > Will you be posting a corresponding Qemu patch for this ?
> > > 
> > > Hi Ashish,
> > > 
> > > as far as I know IBM is working on QEMU patches for guest-based
> > > migration helpers.
> > 
> > Yes, that's right, we'll take on this part.
> > 
> > > However, it would be nice to collaborate on the low-level
> > > (SEC/PEI) firmware patches to detect whether a CPU is part of the
> > > primary VM or the mirror.  If Google has any OVMF patches already
> > > done for that, it would be great to combine it with IBM's SEV
> > > migration code and merge it into upstream OVMF.
> > 
> > We've reached the stage with our prototyping where not having the
> > OVMF support is blocking us from working on QEMU.  If we're going
> > to have to reinvent the wheel in OVMF because Google is unwilling
> > to publish the patches, can you at least give some hints about how
> > you did it?
> > 
> > Thanks,
> > 
> > James
> 
> Hey James,
> It's not strictly necessary to modify OVMF to make SEV VMs live
> migrate. If we were to modify OVMF, we would contribute those changes
> upstream.

Well, no, we already published an OVMF RFC to this list that does
migration.  However, the mirror approach requires a different boot
mechanism for the extra vCPU in the mirror.  I assume you're doing this
bootstrap through OVMF so the hypervisor can interrogate it to get the
correct entry point?  That's the code we're asking to see because
that's what replaces our use of the MP service in the RFC.

James