linux-kernel - Re: [PATCH] x86/sev: Don't hang but terminate on failure to remap SVSM CA

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Message-ID: <11b301d0-d944-a4a2-62e2-8dbc9e37a478@amd.com>
Date: Mon, 6 Jan 2025 10:10:31 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH] x86/sev: Don't hang but terminate on failure to remap
 SVSM CA

On 1/6/25 09:57, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Commit
> 
>   09d35045cd0f  ("x86/sev: Avoid WARN()s and panic()s in early boot code")
> 
> replaced a panic() that could potentially hit before the kernel is even
> mapped with a deadloop, to ensure that execution does not proceed when
> the condition in question hits.
> 
> As Tom suggests, it is better to terminate and return to the hypervisor
> in this case, using a newly invented failure code to describe the
> failure condition.
> 
> Suggested-by: Tom Lendacky <thomas.lendacky@....com>
> Link: https://lore.kernel.org/all/9ce88603-20ca-e644-2d8a-aeeaf79cde69@amd.com
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

Sorry Ard, I hadn't realized that the series was already merged or I
would have submitted the patch myself. Thanks for doing this!

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

> ---
>  arch/x86/coco/sev/core.c          | 4 ++--
>  arch/x86/include/asm/sev-common.h | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index 499b41953e3c..86898547056e 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -2356,8 +2356,8 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
>  	call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
>  	call.rcx = pa;
>  	ret = svsm_perform_call_protocol(&call);
> -	while (ret)
> -		cpu_relax(); /* too early to panic */
> +	if (ret)
> +		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);
>  
>  	RIP_REL_REF(boot_svsm_caa) = (struct svsm_ca *)pa;
>  	RIP_REL_REF(boot_svsm_caa_pa) = pa;
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 50f5666938c0..577b64dda8b4 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -206,6 +206,7 @@ struct snp_psc_desc {
>  #define GHCB_TERM_NO_SVSM		7	/* SVSM is not advertised in the secrets page */
>  #define GHCB_TERM_SVSM_VMPL0		8	/* SVSM is present but has set VMPL to 0 */
>  #define GHCB_TERM_SVSM_CAA		9	/* SVSM is present but CAA is not page aligned */
> +#define GHCB_TERM_SVSM_CA_REMAP_FAIL	10	/* SVSM is present but CA could not be remapped */
>  
>  #define GHCB_RESP_CODE(v)		((v) & GHCB_MSR_INFO_MASK)
>