Re: [PATCH v4 2/5] crypto: ccp: Add support for SNP_FEATURE_INFO command

[Alexey Kardashevskiy <aik@amd.com>]

On 20/5/25 09:56, 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.
> 
> The hypervisor may 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.
> 
> Switch to using SNP platform status instead of SEV platform status if
> SNP is enabled and cache SNP platform status and feature information
> from CPUID 0x8000_0024, sub-function 0, in the sev_device structure.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>   drivers/crypto/ccp/sev-dev.c | 81 ++++++++++++++++++++++++++++++++++++
>   drivers/crypto/ccp/sev-dev.h |  3 ++
>   include/linux/psp-sev.h      | 29 +++++++++++++
>   3 files changed, 113 insertions(+)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 3451bada884e..b642f1183b8b 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -233,6 +233,7 @@ 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 sev_data_snp_feature_info);
>   	default:				return 0;
>   	}
>   
> @@ -1073,6 +1074,69 @@ static void snp_set_hsave_pa(void *arg)
>   	wrmsrq(MSR_VM_HSAVE_PA, 0);
>   }
>   
> +static int snp_get_platform_data(struct sev_user_data_status *status, int *error)
> +{
> +	struct sev_data_snp_feature_info snp_feat_info;
> +	struct sev_device *sev = psp_master->sev_data;
> +	struct snp_feature_info *feat_info;
> +	struct sev_data_snp_addr buf;
> +	struct page *page;
> +	int rc;
> +
> +	/*
> +	 * The output buffer must be firmware page if SEV-SNP is
> +	 * initialized.
> +	 */
> +	if (sev->snp_initialized)
> +		return -EINVAL;
> +
> +	buf.address = __psp_pa(&sev->snp_plat_status);
> +	rc = __sev_do_cmd_locked(SEV_CMD_SNP_PLATFORM_STATUS, &buf, error);
> +
> +	if (rc) {
> +		dev_err(sev->dev, "SNP PLATFORM_STATUS command failed, ret = %d, error = %#x\n",
> +			rc, *error);
> +		return rc;
> +	}
> +
> +	status->api_major = sev->snp_plat_status.api_major;
> +	status->api_minor = sev->snp_plat_status.api_minor;
> +	status->build = sev->snp_plat_status.build_id;
> +	status->state = sev->snp_plat_status.state;

These 4 lines should be ....

> +
> +	/*
> +	 * Do feature discovery of the currently loaded firmware,
> +	 * and cache feature information from CPUID 0x8000_0024,
> +	 * sub-function 0.
> +	 */
> +	if (sev->snp_plat_status.feature_info) {

Could do:

if (!sev->snp_plat_status.feature_info)
	return 0;

and reduce indentation below.

> +		/*
> +		 * Use dynamically allocated structure for the SNP_FEATURE_INFO
> +		 * command to handle any alignment and page boundary check
> +		 * requirements.
> +		 */
> +		page = alloc_page(GFP_KERNEL);
> +		if (!page)
> +			return -ENOMEM;
> +		feat_info = page_address(page);
> +		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;
> +		else
> +			dev_err(sev->dev, "SNP FEATURE_INFO command failed, ret = %d, error = %#x\n",
> +				rc, *error);
> +
> +		__free_page(page);
> +	}
> +
> +	return rc;
> +}
> +
>   static int snp_filter_reserved_mem_regions(struct resource *rs, void *arg)
>   {
>   	struct sev_data_range_list *range_list = arg;
> @@ -1597,6 +1661,23 @@ static int sev_get_api_version(void)
>   	struct sev_user_data_status status;
>   	int error = 0, ret;
>   
> +	/*
> +	 * Use SNP platform status if SNP is enabled and cache
> +	 * SNP platform status and SNP feature information.
> +	 */
> +	if (cc_platform_has(CC_ATTR_HOST_SEV_SNP)) {
> +		ret = snp_get_platform_data(&status, &error);
> +		if (ret) {
> +			dev_err(sev->dev,
> +				"SEV-SNP: failed to get status. Error: %#x\n", error);

Drop this as snp_get_platform_data() does that too (and even better as it prints @ret too).

> +			return 1;
> +		}

.... here, and drop the @status parameter. Which in fact is pointless anyway as ....

Let snp_get_platform_data() do just SNP stuff.


> +	}
> +
> +	/*
> +	 * Fallback to SEV platform status if SNP is not enabled> +	 * or SNP platform status fails.
> +	 */
>   	ret = sev_platform_status(&status, &error);

... this sev_platform_status() is called anyway (not a fallback as the comment above says) and will override whatever snp_get_platform_data() wrote to @status.


>   	if (ret) {
>   		dev_err(sev->dev,
> 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;


"snp_feat_info_0" as 1) it is for SNP like some other fields 2) there is subfunction=1 already defined so need some distinction.


>   };
>   
>   int sev_dev_init(struct psp_device *psp);
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 0b3a36bdaa90..0149d4a6aceb 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;

(not insisting) You could even define this as "struct snp_feature_info_0" with all the bits from "Table 5. Contents of Each Subfunction of Fn8000_0024". Thanks,


> +
>   #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>   
>   /**

-- 
Alexey