Re: [PATCH v2 5/8] x86/sev: Add a function to contain all SEV-specific setup operations

[Ard Biesheuvel]

On Mon, 14 Sep 2026, at 02:57, Melody Wang wrote:
> To make the code clean in the boot phase, add a sev_prepare() wrapper
> which contains early SEV-specific checks in order to have all that code
> in a single place.
>
> No functional changes.
>
> Signed-off-by: Melody Wang <huibo.wang@xxxxxxx>
> ---
>  arch/x86/boot/compressed/sev.c          | 11 +++++++++++
>  arch/x86/include/asm/sev.h              |  3 +++
>  drivers/firmware/efi/libstub/x86-stub.c | 17 +++--------------
>  3 files changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index fc2029746c50..c935a97f72e9 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -511,3 +511,14 @@ bool early_is_sevsnp_guest(void)
>  	}
>  	return true;
>  }
> +
> +bool sev_prepare(void)
> +{
> +	u64 unsupported = snp_get_unsupported_features(sev_get_status());
> +	if (unsupported) {
> +		error("Unsupported SEV-SNP features detected\n");

The EFI stub will call this while running under the boot services, so
error() should not be used here.

Also, error() never returns - it is the decompressor's pseudo-panic()
so whatever you return to will never execute.


> +		return true;
> +	}
> +
> +	return false;
> +}
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 3cb6c5d6a6e0..95f9a5084c45 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -605,6 +605,8 @@ static inline void sev_evict_cache(void *va, int npages)
>  	}
>  }
> 
> +bool sev_prepare(void);
> +
>  #else	/* !CONFIG_AMD_MEM_ENCRYPT */
> 
>  #define snp_vmpl 0
> @@ -652,6 +654,7 @@ static inline enum es_result savic_register_gpa(u64 
> gpa) { return ES_UNSUPPORTED
>  static inline enum es_result savic_unregister_gpa(u64 *gpa) { return 
> ES_UNSUPPORTED; }
>  static inline void sev_apic_ghcb_msr_write(u32 reg, u64 value) { }
>  static inline u64 sev_apic_ghcb_msr_read(u32 reg) { return 0; }
> +static inline bool sev_prepare(void) { return false; }
> 
>  #endif	/* CONFIG_AMD_MEM_ENCRYPT */
> 
> diff --git a/drivers/firmware/efi/libstub/x86-stub.c 
> b/drivers/firmware/efi/libstub/x86-stub.c
> index cef32e2c82d8..fae3a7dfb8b3 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -783,19 +783,6 @@ static efi_status_t exit_boot(struct boot_params 
> *boot_params, void *handle)
>  	return EFI_SUCCESS;
>  }
> 
> -static bool have_unsupported_snp_features(void)
> -{
> -	u64 unsupported;
> -
> -	unsupported = snp_get_unsupported_features(sev_get_status());
> -	if (unsupported) {
> -		efi_err("Unsupported SEV-SNP features detected: 0x%llx\n",
> -			unsupported);
> -		return true;
> -	}
> -	return false;
> -}
> -
>  static void efi_get_seed(void *seed, int size)
>  {
>  	efi_get_random_bytes(size, seed);
> @@ -919,6 +906,7 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
>  	unsigned long kernel_entry;
>  	struct setup_header *hdr;
>  	efi_status_t status;
> +	bool err;
> 
>  	efi_system_table = sys_table_arg;
>  	/* Check if we were booted by the EFI firmware */
> @@ -933,7 +921,8 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
> 
>  	hdr = &boot_params->hdr;
> 
> -	if (have_unsupported_snp_features())
> +	err = sev_prepare();
> +	if (err)
>  		efi_exit(handle, EFI_UNSUPPORTED);
> 
>  	if (IS_ENABLED(CONFIG_EFI_DXE_MEM_ATTRIBUTES)) {
> -- 
> 2.43.0