linux-kernel - Re: [RFT PATCH v3 02/21] x86/sev: Use MSR protocol for remapping SVSM calling area

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Message-ID: <20250515164337.GDaCYZuXXjJkfRlK8k@fat_crate.local>
Date: Thu, 15 May 2025 18:43:37 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, x86@...nel.org,
	Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Dionna Amalie Glaze <dionnaglaze@...gle.com>,
	Kevin Loughlin <kevinloughlin@...gle.com>,
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFT PATCH v3 02/21] x86/sev: Use MSR protocol for remapping
 SVSM calling area

On Mon, May 12, 2025 at 09:08:37PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> As the preceding code comment already indicates, remapping the SVSM
> calling area occurs long before the GHCB page is configured, and so
> calling svsm_perform_call_protocol() is guaranteed to result in a call
> to svsm_perform_msr_protocol().
> 
> So just call the latter directly. This allows most of the GHCB based API
> infrastructure to be moved out of the startup code in a subsequent
> patch.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/x86/boot/startup/sev-startup.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
> index 435853a55768..a1d5a5632d58 100644
> --- a/arch/x86/boot/startup/sev-startup.c
> +++ b/arch/x86/boot/startup/sev-startup.c
> @@ -325,7 +325,9 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
>  	call.caa = svsm_get_caa();
>  	call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
>  	call.rcx = pa;
> -	ret = svsm_perform_call_protocol(&call);
> +	do {
> +		ret = svsm_perform_msr_protocol(&call);
> +	} while (ret == -EAGAIN);

Right, a future cleanup for another patch would be to wrap that loop into
a function. But not now.

>  	if (ret)
>  		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);
>  
> -- 

Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette