linux-kernel - Re: [PATCH] x86/boot/sev: Support memory acceptance in the EFI stub under SVSM

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Message-ID: <aBcZe1amYvqslhvA@gmail.com>
Date: Sun, 4 May 2025 09:38:35 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Tom Lendacky <thomas.lendacky@....com>,
	Ard Biesheuvel <ardb+git@...gle.com>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>,
	Dionna Amalie Glaze <dionnaglaze@...gle.com>,
	Kevin Loughlin <kevinloughlin@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/boot/sev: Support memory acceptance in the EFI stub
 under SVSM


* Ard Biesheuvel <ardb@...nel.org> wrote:

> On Thu, 1 May 2025 at 20:05, Tom Lendacky <thomas.lendacky@....com> wrote:
> >
> > On 4/28/25 12:43, Ard Biesheuvel wrote:
> > > From: Ard Biesheuvel <ardb@...nel.org>
> > >
> > > Commit
> > >
> > >   d54d610243a4 ("x86/boot/sev: Avoid shared GHCB page for early memory acceptance")
> > >
> > > provided a fix for SEV-SNP memory acceptance from the EFI stub when
> > > running at VMPL #0. However, that fix was insufficient for SVSM SEV-SNP
> > > guests running at VMPL >0, as those rely on a SVSM calling area, which
> > > is a shared buffer whose address is programmed into a SEV-SNP MSR, and
> > > the SEV init code that sets up this calling area executes much later
> > > during the boot.
> > >
> > > Given that booting via the EFI stub at VMPL >0 implies that the firmware
> > > has configured this calling area already, reuse it for performing memory
> > > acceptance in the EFI stub.
> >
> > This looks to be working for SNP guest boot and kexec. SNP guest boot with
> > an SVSM is also working, but kexec isn't. But the kexec failure of an SVSM
> > SNP guest is unrelated to this patch, I'll send a fix for that separately.
> >
> 
> Thanks for confirming.
> 
> Ingo, Boris, can we get this queued as a fix, please, and merge it
> back into x86/boot as was done before?

Just to clarify, memory acceptance trough the EFI stub from VMPL >0 
SEV-SNP guests was broken last summer via fcd042e86422, and it hasn't 
worked since then?

Thanks,

	Ingo