linux-kernel - Re: [PATCH v2 0/9] Move initializing SEV/SNP functionality to KVM

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Message-ID: <Z2HvJESqpc7Gd-dG@google.com>
Date: Tue, 17 Dec 2024 13:37:40 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Ashish Kalra <ashish.kalra@....com>
Cc: Dionna Amalie Glaze <dionnaglaze@...gle.com>, pbonzini@...hat.com, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	hpa@...or.com, thomas.lendacky@....com, john.allen@....com, 
	herbert@...dor.apana.org.au, davem@...emloft.net, michael.roth@....com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-crypto@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v2 0/9] Move initializing SEV/SNP functionality to KVM

On Tue, Dec 17, 2024, Ashish Kalra wrote:
> 
> 
> On 12/17/2024 10:00 AM, Dionna Amalie Glaze wrote:
> > On Mon, Dec 16, 2024 at 3:57 PM Ashish Kalra <Ashish.Kalra@....com> wrote:
> >>
> >> From: Ashish Kalra <ashish.kalra@....com>
> > 
> >> The on-demand SEV initialization support requires a fix in QEMU to
> >> remove check for SEV initialization to be done prior to launching
> >> SEV/SEV-ES VMs.
> >> NOTE: With the above fix for QEMU, older QEMU versions will be broken
> >> with respect to launching SEV/SEV-ES VMs with the newer kernel/KVM as
> >> older QEMU versions require SEV initialization to be done before
> >> launching SEV/SEV-ES VMs.
> >>
> > 
> > I don't think this is okay. I think you need to introduce a KVM
> > capability to switch over to the new way of initializing SEV VMs and
> > deprecate the old way so it doesn't need to be supported for any new
> > additions to the interface.
> > 
> 
> But that means KVM will need to support both mechanisms of doing SEV
> initialization - during KVM module load time and the deferred/lazy
> (on-demand) SEV INIT during VM launch.

What's the QEMU change?  Dionna is right, we can't break userspace, but maybe
there's an alternative to supporting both models.