From: Mike Larkin <mlarkin@nested.page>
Subject: Re: SEV-ES guest: Only claim early GHCB pages when we actuall are SEV-ES guest
To: Alexander Bluhm <bluhm@openbsd.org>
Cc: tech@openbsd.org
Date: Fri, 11 Jul 2025 09:30:25 -0700

On Thu, Jul 03, 2025 at 12:56:01PM +0200, Alexander Bluhm wrote:
> On Wed, Jul 02, 2025 at 11:47:12AM -0700, Mike Larkin wrote:
> > On Tue, Jul 01, 2025 at 10:37:57AM +0200, Hans-J?rg H?xer wrote:
> > > Hi,
> > >
> > > as suggested by bluhm@, only claim GHCB pages when we are actually
> > > running SEV-ES guest mode.
> > >
> >
> > I think this is overoptimization but ok mlarkin if this is the way
> > you want to head.
>
> When I was reading the code, I was wondering why first_avail is
> incremented.  For me it is clearer if we put it within the
> if(SEV_STAT_ES_ENABLED).
>
> It is not about saving 8 KB.  For me the intension is clearer.  But
> I don't insist on that if you have the opposit impression.
>
> bluhm
>

ok, no worries :)

-ml

> > > ---
> > > commit d2444d09c945baad0e5d9283a50d466d7de7b400
> > > Author: Hans-Joerg Hoexer <hshoexer@genua.de>
> > > Date:   Mon Jun 30 15:29:35 2025 +0200
> > >
> > >     SEV-ES guest: Only claim early GHCB pages when we actuall are SEV-ES guest
> > >
> > > diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
> > > index 9b0badd610d..e0e8862d375 100644
> > > --- a/sys/arch/amd64/amd64/machdep.c
> > > +++ b/sys/arch/amd64/amd64/machdep.c
> > > @@ -1470,9 +1470,10 @@ init_x86_64(paddr_t first_avail)
> > >  	/*
> > >  	 * locore0 mapped 2 pages for use as GHCB before pmap is initialized.
> > >  	 */
> > > -	if (ISSET(cpu_sev_guestmode, SEV_STAT_ES_ENABLED))
> > > +	if (ISSET(cpu_sev_guestmode, SEV_STAT_ES_ENABLED)) {
> > >  		cpu_init_early_vctrap(first_avail);
> > > -	first_avail += 2 * NBPG;
> > > +		first_avail += 2 * NBPG;
> > > +	}
> > >
> > >  	/*
> > >  	 * locore0 mapped 3 pages for use before the pmap is initialized
> >
>