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

[Kalra, Ashish]

Hello Tom,

On 10/2/2024 4:19 PM, Tom Lendacky wrote:
> On 10/2/24 16:18, Tom Lendacky wrote:
>> 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?
> Although, as I hit send I realized that we only do DOWNLOAD_FIRMWARE
> before SNP is initialized (currently).

We do have DOWNLOAD_FIRMWARE_EX support coming up which can/will happen after SNP_INIT, but there we can still use SEV's PLATFORM_DATA command to get (updated) SEV/SNP firmware version.

Thanks, Ashish

>
> 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
>>>  
>>>  /**