linux-kernel - Re: [PATCH v6 03/22] x86/sev: Use MSR protocol only for early SVSM PVALIDATE call

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Message-ID: <6bf4402b-7a16-d111-a5a1-fbf15edfd7b9@amd.com>
Date: Tue, 29 Jul 2025 08:48:29 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org
Cc: linux-efi@...r.kernel.org, x86@...nel.org,
 Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>,
 Ingo Molnar <mingo@...nel.org>, Kevin Loughlin <kevinloughlin@...gle.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Nikunj A Dadhania <nikunj@....com>
Subject: Re: [PATCH v6 03/22] x86/sev: Use MSR protocol only for early SVSM
 PVALIDATE call

On 7/22/25 02:27, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> The early page state change API performs an SVSM call to PVALIDATE each
> page when running under a SVSM, and this involves either a GHCB page
> based call or a call based on the MSR protocol.
> 
> The GHCB page based variant involves VA to PA translation of the GHCB
> address, and this is best avoided in the startup code, where virtual
> addresses are ambiguous (1:1 or kernel virtual).
> 
> As this is the last remaining occurrence of svsm_perform_call_protocol()
> in the startup code, switch to the MSR protocol exclusively in this
> particular case, so that the GHCB based plumbing can be moved out of the
> startup code entirely in a subsequent patch.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/boot/compressed/sev.c     | 20 --------------------
>  arch/x86/boot/startup/sev-shared.c |  9 ++++++---
>  2 files changed, 6 insertions(+), 23 deletions(-)
>