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

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On 10/2/24 16:40, Kalra, Ashish wrote:
> 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.

But you probably also want to get updated platform data, too. So I would
think you would want to be able to call this routine again, post SNP_INIT.

Thanks,
Tom

> 
> 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
>>>>  
>>>>  /**




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