linux-kernel - Re: [PATCH v5 02/22] x86/sev: Use MSR protocol for remapping SVSM calling area

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Message-ID: <d750dec4-f68f-0f3d-69cd-53749044ecba@amd.com>
Date: Wed, 16 Jul 2025 12:03:43 -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 v5 02/22] x86/sev: Use MSR protocol for remapping SVSM
 calling area

On 7/15/25 22:18, 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>
> Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/boot/startup/sev-shared.c  | 11 +++++++++++
>  arch/x86/boot/startup/sev-startup.c |  5 ++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c
> index c401d0391537..60ab09b3149d 100644
> --- a/arch/x86/boot/startup/sev-shared.c
> +++ b/arch/x86/boot/startup/sev-shared.c
> @@ -723,6 +723,17 @@ static void __head setup_cpuid_table(const struct cc_blob_sev_info *cc_info)
>  	}
>  }
>  
> +static int __head svsm_call_msr_protocol(struct svsm_call *call)
> +{
> +	int ret;
> +
> +	do {
> +		ret = svsm_perform_msr_protocol(call);
> +	} while (ret == -EAGAIN);
> +
> +	return ret;
> +}
> +
>  static void __head svsm_pval_4k_page(unsigned long paddr, bool validate)
>  {
>  	struct svsm_pvalidate_call *pc;
> diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
> index 0b7e3b950183..c30e0eed0131 100644
> --- a/arch/x86/boot/startup/sev-startup.c
> +++ b/arch/x86/boot/startup/sev-startup.c
> @@ -295,7 +295,6 @@ static __head struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
>  static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
>  {
>  	struct svsm_call call = {};
> -	int ret;
>  	u64 pa;
>  
>  	/*
> @@ -325,8 +324,8 @@ 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);
> -	if (ret)
> +
> +	if (svsm_perform_msr_protocol(&call))

This should be svsm_call_msr_protocol().

Thanks,
Tom

>  		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);
>  
>  	boot_svsm_caa = (struct svsm_ca *)pa;