Re: [PATCH v4 1/7] x86/sev: Avoid WARN()s and panic()s in early boot code

[Tom Lendacky <thomas.lendacky@amd.com>]

On 12/5/24 05:28, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> Using WARN() or panic() while executing from the early 1:1 mapping is
> unlikely to do anything useful: the string literals are passed using
> their kernel virtual addresses which are not even mapped yet. But even
> if they were, calling into the printk() machinery from the early 1:1
> mapped code is not going to get very far.
> 
> So drop the WARN()s entirely, and replace panic() with a deadloop.
> 
> Link: https://lore.kernel.org/all/6904c198-9047-14bb-858e-38b531589379@amd.com/T/#u
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/x86/coco/sev/core.c   | 15 +++++----------
>  arch/x86/coco/sev/shared.c |  9 +++++----
>  2 files changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index c5b0148b8c0a..499b41953e3c 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -777,15 +777,10 @@ early_set_pages_state(unsigned long vaddr, unsigned long paddr,
>  
>  		val = sev_es_rd_ghcb_msr();
>  
> -		if (WARN(GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP,
> -			 "Wrong PSC response code: 0x%x\n",
> -			 (unsigned int)GHCB_RESP_CODE(val)))
> +		if (GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP)
>  			goto e_term;
>  
> -		if (WARN(GHCB_MSR_PSC_RESP_VAL(val),
> -			 "Failed to change page state to '%s' paddr 0x%lx error 0x%llx\n",
> -			 op == SNP_PAGE_STATE_PRIVATE ? "private" : "shared",
> -			 paddr, GHCB_MSR_PSC_RESP_VAL(val)))
> +		if (GHCB_MSR_PSC_RESP_VAL(val))
>  			goto e_term;
>  
>  		/* Page validation must be performed after changing to private */
> @@ -821,7 +816,7 @@ void __head early_snp_set_memory_private(unsigned long vaddr, unsigned long padd
>  	early_set_pages_state(vaddr, paddr, npages, SNP_PAGE_STATE_PRIVATE);
>  }
>  
> -void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
> +void __head early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
>  					unsigned long npages)
>  {
>  	/*
> @@ -2361,8 +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);
> -	if (ret)
> -		panic("Can't remap the SVSM CA, ret=%d, rax_out=0x%llx\n", ret, call.rax_out);
> +	while (ret)
> +		cpu_relax(); /* too early to panic */

We should give some indication of the error and call sev_es_terminate()
here with a new reason code, something like:

sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);

Thanks,
Tom

>  
>  	RIP_REL_REF(boot_svsm_caa) = (struct svsm_ca *)pa;
>  	RIP_REL_REF(boot_svsm_caa_pa) = pa;
> diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
> index 71de53194089..afb7ffc355fe 100644
> --- a/arch/x86/coco/sev/shared.c
> +++ b/arch/x86/coco/sev/shared.c
> @@ -1243,7 +1243,7 @@ static void svsm_pval_terminate(struct svsm_pvalidate_call *pc, int ret, u64 svs
>  	__pval_terminate(pfn, action, page_size, ret, svsm_ret);
>  }
>  
> -static void svsm_pval_4k_page(unsigned long paddr, bool validate)
> +static void __head svsm_pval_4k_page(unsigned long paddr, bool validate)
>  {
>  	struct svsm_pvalidate_call *pc;
>  	struct svsm_call call = {};
> @@ -1275,12 +1275,13 @@ static void svsm_pval_4k_page(unsigned long paddr, bool validate)
>  
>  	ret = svsm_perform_call_protocol(&call);
>  	if (ret)
> -		svsm_pval_terminate(pc, ret, call.rax_out);
> +		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PVALIDATE);
>  
>  	native_local_irq_restore(flags);
>  }
>  
> -static void pvalidate_4k_page(unsigned long vaddr, unsigned long paddr, bool validate)
> +static void __head pvalidate_4k_page(unsigned long vaddr, unsigned long paddr,
> +				     bool validate)
>  {
>  	int ret;
>  
> @@ -1293,7 +1294,7 @@ static void pvalidate_4k_page(unsigned long vaddr, unsigned long paddr, bool val
>  	} else {
>  		ret = pvalidate(vaddr, RMP_PG_SIZE_4K, validate);
>  		if (ret)
> -			__pval_terminate(PHYS_PFN(paddr), validate, RMP_PG_SIZE_4K, ret, 0);
> +			sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PVALIDATE);
>  	}
>  }
>