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Message-ID: <48e2199f-37e4-4ea1-b28b-23eb421444cc@amd.com>
Date: Thu, 5 Jun 2025 14:49:11 +1000
From: Alexey Kardashevskiy <aik@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, seanjc@...gle.com,
pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com, herbert@...dor.apana.org.au
Cc: x86@...nel.org, john.allen@....com, davem@...emloft.net,
thomas.lendacky@....com, michael.roth@....com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH v4 2/5] crypto: ccp: Add support for SNP_FEATURE_INFO
command
On 20/5/25 09:56, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....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@....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
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