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

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

On 10/2/24 16:18, Tom Lendacky wrote:
> On 9/17/24 15:16, Ashish Kalra wrote:
>> From: Ashish Kalra <ashish.kalra@amd.com>
>>
>> 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@amd.com>
>> ---
>>  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?

Although, as I hit send I realized that we only do DOWNLOAD_FIRMWARE
before SNP is initialized (currently).

Thanks,
Tom

> 
> 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
>>  
>>  /**