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

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Message-ID: <CAMj1kXE7=u9xNcUHiyFVPbOpwPvntFjdLfTzD0LeD_7it2MEQg@mail.gmail.com>
Date: Fri, 2 May 2025 15:11:21 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, x86@...nel.org, Borislav Petkov <bp@...en8.de>, 
	Ingo Molnar <mingo@...nel.org>, 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

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?


> Thanks,
> Tom
>
> >
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Dionna Amalie Glaze <dionnaglaze@...gle.com>
> > Cc: Kevin Loughlin <kevinloughlin@...gle.com>
> > Cc: <stable@...r.kernel.org>
> > Fixes: fcd042e86422 ("x86/sev: Perform PVALIDATE using the SVSM when not at VMPL0")
> > Co-developed-by: Tom Lendacky <thomas.lendacky@....com>
> > Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > ---
> > Tom,
> >
> > Please confirm that this works as you intended.
> >
> > Thanks,
> >