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From: Kevin Loughlin <kevinloughlin@google.com>
Date: Sun, 10 Mar 2024 10:12:32 -0700
Message-ID: <CAGdbjmKC+tTBHLPZ6bqCXvu45Gbout+0QrNemDqxY-nKAo_3gg@mail.gmail.com>
Subject: Re: [PATCH v2] x86/kernel: skip ROM range scans and validation for
 SEV-SNP guests
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>, acdunlap@google.com, alexander.shishkin@linux.intel.com, 
	andrisaar@google.com, bhe@redhat.com, brijesh.singh@amd.com, 
	dave.hansen@linux.intel.com, dionnaglaze@google.com, grobler@google.com, 
	hpa@zytor.com, jacobhxu@google.com, jpoimboe@kernel.org, kai.huang@intel.com, 
	linux-kernel@vger.kernel.org, michael.roth@amd.com, mingo@redhat.com, 
	peterz@infradead.org, pgonda@google.com, ross.lagerwall@citrix.com, 
	sidtelang@google.com, tglx@linutronix.de, thomas.lendacky@amd.com, 
	x86@kernel.org, ytcoode@gmail.com
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On Fri, Mar 8, 2024 at 3:44=E2=80=AFAM Ard Biesheuvel <ardb@kernel.org> wro=
te:
>
> On Fri, 8 Mar 2024 at 12:01, Borislav Petkov <bp@alien8.de> wrote:
> >
> > On Fri, Mar 08, 2024 at 11:30:50AM +0100, Ard Biesheuvel wrote:
> > > Agree with the analysis and the conclusion. However, this will need t=
o
> > > be split into generic and x86 specific changes, given that the DMI
> > > code is shared between all architectures, and explicitly checking for
> > > SEV-SNP support in generic code is not appropriate.
> > >
> > > So what we will need is:
> >
> > I was actually thinking of:
> >
> >         x86_init.resources.probe_roms =3D snp_probe_roms;
> >
> > and snp_probe_roms() is an empty stub.
> >
> > Problem solved without ugly sprinkling of checks everywhere.
> >
>
> Indeed. Setting the override could be done in
> init_hypervisor_platform(), which is called right before from
> setup_arch().

The call to init_hypervisor_platform() has a comment saying it must
come after dmi_setup() (i.e., init_hypervisor_platform() would *not*
work for doing a dmi_setup() override), so I'm currently planning to
do the overrides at the end of snp_init() in arch/x86/kernel/sev.c
instead (which comes before both). This would be somewhat similar to
how there are early setup functions for specific platforms that
perform init overrides for different reasons (example:
x86_ce4100_early_setup()). Open to other locations of course.