Re: [PATCH v2 2/3] crypto: ccp: Add support for SNP_FEATURE_INFO command

[Tom Lendacky]

On 9/17/24 15:16, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
> 
> The FEATURE_INFO command provides host and guests a programmatic means
> to learn about the supported features of the currently loaded firmware.
> FEATURE_INFO command leverages the same mechanism as the CPUID instruction.
> Instead of using the CPUID instruction to retrieve Fn8000_0024,
> software can use FEATURE_INFO.
> 
> Host/Hypervisor would use the FEATURE_INFO command, while guests would
> actually issue the CPUID instruction.
> 
> The hypervisor can provide Fn8000_0024 values to the guest via the CPUID
> page in SNP_LAUNCH_UPDATE. As with all CPUID output recorded in that page,
> the hypervisor can filter Fn8000_0024. The firmware will examine
> Fn8000_0024 and apply its CPUID policy.
> 
> During CCP module initialization, after firmware update, the SNP
> platform status and feature information from CPUID 0x8000_0024,
> sub-function 0, are cached in the sev_device structure.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> ---
>  drivers/crypto/ccp/sev-dev.c | 47 ++++++++++++++++++++++++++++++++++++
>  drivers/crypto/ccp/sev-dev.h |  3 +++
>  include/linux/psp-sev.h      | 29 ++++++++++++++++++++++
>  3 files changed, 79 insertions(+)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index af018afd9cd7..564daf748293 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -223,6 +223,7 @@ static int sev_cmd_buffer_len(int cmd)
>  	case SEV_CMD_SNP_GUEST_REQUEST:		return sizeof(struct sev_data_snp_guest_request);
>  	case SEV_CMD_SNP_CONFIG:		return sizeof(struct sev_user_data_snp_config);
>  	case SEV_CMD_SNP_COMMIT:		return sizeof(struct sev_data_snp_commit);
> +	case SEV_CMD_SNP_FEATURE_INFO:		return sizeof(struct snp_feature_info);
>  	default:				return 0;
>  	}
>  
> @@ -1063,6 +1064,50 @@ static void snp_set_hsave_pa(void *arg)
>  	wrmsrl(MSR_VM_HSAVE_PA, 0);
>  }
>  
> +static void snp_get_platform_data(void)
> +{
> +	struct sev_device *sev = psp_master->sev_data;
> +	struct sev_data_snp_feature_info snp_feat_info;
> +	struct snp_feature_info *feat_info;
> +	struct sev_data_snp_addr buf;
> +	int error = 0, rc;
> +
> +	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> +		return;
> +
> +	/*
> +	 * The output buffer must be firmware page if SEV-SNP is
> +	 * initialized.

This comment is a little confusing relative to the "if" check that is
performed. Add some more detail about what this check is for.

But... would this ever need to be called after SNP_INIT? Would we want
to call this again after, say, a DOWNLOAD_FIRMWARE command?

Thanks,
Tom

> +	 */
> +	if (sev->snp_initialized)
> +		return;
> +
> +	buf.address = __psp_pa(&sev->snp_plat_status);
> +	rc = __sev_do_cmd_locked(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error);
> +
> +	/*
> +	 * Do feature discovery of the currently loaded firmware,
> +	 * and cache feature information from CPUID 0x8000_0024,
> +	 * sub-function 0.
> +	 */
> +	if (!rc && sev->snp_plat_status.feature_info) {
> +		/*
> +		 * Use dynamically allocated structure for the SNP_FEATURE_INFO
> +		 * command to handle any alignment and page boundary check
> +		 * requirements.
> +		 */
> +		feat_info = kzalloc(sizeof(*feat_info), GFP_KERNEL);
> +		snp_feat_info.length = sizeof(snp_feat_info);
> +		snp_feat_info.ecx_in = 0;
> +		snp_feat_info.feature_info_paddr = __psp_pa(feat_info);
> +
> +		rc = __sev_do_cmd_locked(SEV_CMD_SNP_FEATURE_INFO, &snp_feat_info, &error);
> +		if (!rc)
> +			sev->feat_info = *feat_info;
> +		kfree(feat_info);
> +	}
> +}
> +
>  static int snp_filter_reserved_mem_regions(struct resource *rs, void *arg)
>  {
>  	struct sev_data_range_list *range_list = arg;
> @@ -2415,6 +2460,8 @@ void sev_pci_init(void)
>  			 api_major, api_minor, build,
>  			 sev->api_major, sev->api_minor, sev->build);
>  
> +	snp_get_platform_data();
> +
>  	/* Initialize the platform */
>  	args.probe = true;
>  	rc = sev_platform_init(&args);
> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
> index 3e4e5574e88a..1c1a51e52d2b 100644
> --- a/drivers/crypto/ccp/sev-dev.h
> +++ b/drivers/crypto/ccp/sev-dev.h
> @@ -57,6 +57,9 @@ struct sev_device {
>  	bool cmd_buf_backup_active;
>  
>  	bool snp_initialized;
> +
> +	struct sev_user_data_snp_status snp_plat_status;
> +	struct snp_feature_info feat_info;
>  };
>  
>  int sev_dev_init(struct psp_device *psp);
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 903ddfea8585..6068a89839e1 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -107,6 +107,7 @@ enum sev_cmd {
>  	SEV_CMD_SNP_DOWNLOAD_FIRMWARE_EX = 0x0CA,
>  	SEV_CMD_SNP_COMMIT		= 0x0CB,
>  	SEV_CMD_SNP_VLEK_LOAD		= 0x0CD,
> +	SEV_CMD_SNP_FEATURE_INFO	= 0x0CE,
>  
>  	SEV_CMD_MAX,
>  };
> @@ -812,6 +813,34 @@ struct sev_data_snp_commit {
>  	u32 len;
>  } __packed;
>  
> +/**
> + * struct sev_data_snp_feature_info - SEV_SNP_FEATURE_INFO structure
> + *
> + * @length: len of the command buffer read by the PSP
> + * @ecx_in: subfunction index
> + * @feature_info_paddr : SPA of the FEATURE_INFO structure
> + */
> +struct sev_data_snp_feature_info {
> +	u32 length;
> +	u32 ecx_in;
> +	u64 feature_info_paddr;
> +} __packed;
> +
> +/**
> + * struct feature_info - FEATURE_INFO structure
> + *
> + * @eax: output of SNP_FEATURE_INFO command
> + * @ebx: output of SNP_FEATURE_INFO command
> + * @ecx: output of SNP_FEATURE_INFO command
> + * #edx: output of SNP_FEATURE_INFO command
> + */
> +struct snp_feature_info {
> +	u32 eax;
> +	u32 ebx;
> +	u32 ecx;
> +	u32 edx;
> +} __packed;
> +
>  #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>  
>  /**