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Message-ID: <46810e8f-eba7-69ac-e4ae-009c379aa960@amd.com>
Date: Tue, 15 Jul 2025 11:23:00 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, corbet@....net, seanjc@...gle.com,
pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
john.allen@....com, herbert@...dor.apana.org.au, davem@...emloft.net,
akpm@...ux-foundation.org, rostedt@...dmis.org, paulmck@...nel.org
Cc: nikunj@....com, Neeraj.Upadhyay@....com, aik@....com, ardb@...nel.org,
michael.roth@....com, arnd@...db.de, linux-doc@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org
Subject: Re: [PATCH v6 3/7] crypto: ccp - Add support for SNP_FEATURE_INFO
command
On 7/14/25 17:39, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
>
> The FEATURE_INFO command provides hypervisors with a programmatic means
> to learn about the supported features of the currently loaded firmware.
> This command mimics the CPUID instruction relative to sub-leaf input and
> the four unsigned integer output values. To obtain information
> regarding the features present in the currently loaded SEV firmware,
> use the SNP_FEATURE_INFO command.
>
> Cache the SNP platform status and feature information from CPUID
> 0x8000_0024 in the sev_device structure. If SNP is enabled, utilize
> this cached SNP platform status for the API major, minor and build
> version.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
with a minor comment below.
> ---
> drivers/crypto/ccp/sev-dev.c | 72 ++++++++++++++++++++++++++++++++++++
> drivers/crypto/ccp/sev-dev.h | 3 ++
> include/linux/psp-sev.h | 29 +++++++++++++++
> 3 files changed, 104 insertions(+)
>
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 528013be1c0a..8f4e22751bc4 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 +1074,67 @@ static void snp_set_hsave_pa(void *arg)
> wrmsrq(MSR_VM_HSAVE_PA, 0);
> }
>
> +static int snp_get_platform_data(struct sev_device *sev, int *error)
> +{
> + struct sev_data_snp_feature_info snp_feat_info;
> + struct snp_feature_info *feat_info;
> + struct sev_data_snp_addr buf;
> + struct page *page;
> + int rc;
> +
> + /*
> + * This function is expected to be called before SNP is not
s/not//
Someone else had made that comment, looks like you missed it.
Thanks,
Tom
> + * initialized.
> + */
> + if (sev->snp_initialized)
> + return -EINVAL;
> +
> + buf.address = __psp_pa(&sev->snp_plat_status);
> + rc = sev_do_cmd(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;
> + }
> +
> + sev->api_major = sev->snp_plat_status.api_major;
> + sev->api_minor = sev->snp_plat_status.api_minor;
> + sev->build = sev->snp_plat_status.build_id;
> +
> + /*
> + * 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)
> + return 0;
> +
> + /*
> + * Use dynamically allocated structure for the SNP_FEATURE_INFO
> + * command to ensure structure is 8-byte aligned, and does not
> + * cross a page boundary.
> + */
> + 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(SEV_CMD_SNP_FEATURE_INFO, &snp_feat_info, error);
> + if (!rc)
> + sev->snp_feat_info_0 = *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;
> @@ -1599,6 +1661,16 @@ static int sev_get_api_version(void)
> struct sev_user_data_status status;
> int error = 0, ret;
>
> + /*
> + * Cache SNP platform status and SNP feature information
> + * if SNP is available.
> + */
> + if (cc_platform_has(CC_ATTR_HOST_SEV_SNP)) {
> + ret = snp_get_platform_data(sev, &error);
> + if (ret)
> + return 1;
> + }
> +
> ret = sev_platform_status(&status, &error);
> if (ret) {
> dev_err(sev->dev,
> diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
> index 24dd8ff8afaa..5aed2595c9ae 100644
> --- a/drivers/crypto/ccp/sev-dev.h
> +++ b/drivers/crypto/ccp/sev-dev.h
> @@ -58,6 +58,9 @@ struct sev_device {
> bool snp_initialized;
>
> struct sev_user_data_status sev_plat_status;
> +
> + struct sev_user_data_snp_status snp_plat_status;
> + struct snp_feature_info snp_feat_info_0;
> };
>
> int sev_dev_init(struct psp_device *psp);
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 0f5f94137f6d..5fb6ae0f51cc 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,
> };
> @@ -814,6 +815,34 @@ 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 : System Physical Address 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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