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Re: [PATCH v7 07/13] confidential guest support: Introduce cgs "ready" f

From: Cornelia Huck
Subject: Re: [PATCH v7 07/13] confidential guest support: Introduce cgs "ready" flag
Date: Tue, 19 Jan 2021 09:16:08 +0100

On Mon, 18 Jan 2021 19:47:30 +0000
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:

> * David Gibson (david@gibson.dropbear.id.au) wrote:
> > The platform specific details of mechanisms for implementing
> > confidential guest support may require setup at various points during
> > initialization.  Thus, it's not really feasible to have a single cgs
> > initialization hook, but instead each mechanism needs its own
> > initialization calls in arch or machine specific code.
> > 
> > However, to make it harder to have a bug where a mechanism isn't
> > properly initialized under some circumstances, we want to have a
> > common place, relatively late in boot, where we verify that cgs has
> > been initialized if it was requested.
> > 
> > This patch introduces a ready flag to the ConfidentialGuestSupport
> > base type to accomplish this, which we verify just before the machine
> > specific initialization function.  
> You may find you need to define 'ready' and the answer might be a bit
> variable; for example, on SEV there's a setup bit and then you may end
> up doing an attestation and receiving some data before you actaully let
> the guest execute code.   Is it ready before it's received the
> attestation response or only when it can run code?
> Is a Power or 390 machine 'ready' before it's executed the magic
> instruction to enter the confidential mode?

I would consider those machines where the guest makes the transition
itself "ready" as soon as everything is set up so that the guest can
actually initiate the transition. Otherwise, those machines would never
be "ready" if the guest does not transition.

Maybe we can define "ready" as "the guest can start to execute in
secure mode", where "guest" includes the bootloader and everything that
runs in a guest context, and "start to execute" implies that some setup
may be done only after the guest has kicked it off?

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