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

From: Tom Lendacky
Date: Wed Oct 02 2024 - 17:49:40 EST

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In reply to: Kalra, Ashish: "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
>>>>
>>>> /**

Next message: Dan Williams: "Re: [PATCH] driver core: Fix userspace expectations of uevent_show() as a probe barrier"
Previous message: Bert Karwatzki: "Re: [PATCH v8 14/21] mm/mmap: Avoid zeroing vma tree in mmap_region()"
In reply to: Kalra, Ashish: "Re: [PATCH v2 2/3] crypto: ccp: Add support for SNP_FEATURE_INFO command"
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