Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

[Tom Lendacky <thomas.lendacky@amd.com>]

On 2/23/23 15:41, Zhi Wang wrote:
> On Mon, 20 Feb 2023 12:38:25 -0600
> Michael Roth <michael.roth@amd.com> wrote:
> 
>> From: Brijesh Singh <brijesh.singh@amd.com>
>>
>> KVM_SEV_SNP_LAUNCH_START begins the launch process for an SEV-SNP guest.
>> The command initializes a cryptographic digest context used to construct
>> the measurement of the guest. If the guest is expected to be migrated,
>> the command also binds a migration agent (MA) to the guest.
>>
>> For more information see the SEV-SNP specification.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
>> Signed-off-by: Michael Roth <michael.roth@amd.com>
>> ---
>>   .../virt/kvm/x86/amd-memory-encryption.rst    |  24 ++++
>>   arch/x86/kvm/svm/sev.c                        | 121 +++++++++++++++++-
>>   arch/x86/kvm/svm/svm.h                        |   1 +
>>   include/uapi/linux/kvm.h                      |  10 ++
>>   4 files changed, 153 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> index 2432213bd0ea..58971fc02a15 100644
>> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> @@ -461,6 +461,30 @@ The flags bitmap is defined as::
>>   If the specified flags is not supported then return -EOPNOTSUPP, and the supported
>>   flags are returned.
>>   
>> +19. KVM_SNP_LAUNCH_START
>> +------------------------
>> +
>> +The KVM_SNP_LAUNCH_START command is used for creating the memory encryption
>> +context for the SEV-SNP guest. To create the encryption context, user must
>> +provide a guest policy, migration agent (if any) and guest OS visible
>> +workarounds value as defined SEV-SNP specification.
>> +
>> +Parameters (in): struct  kvm_snp_launch_start
>> +
>> +Returns: 0 on success, -negative on error
>> +
>> +::
>> +
>> +        struct kvm_sev_snp_launch_start {
>> +                __u64 policy;           /* Guest policy to use. */
>> +                __u64 ma_uaddr;         /* userspace address of migration agent */
>> +                __u8 ma_en;             /* 1 if the migration agent is enabled */
>> +                __u8 imi_en;            /* set IMI to 1. */
>> +                __u8 gosvw[16];         /* guest OS visible workarounds */
>> +        };
>> +
>> +See the SEV-SNP specification for further detail on the launch input.
>> +
>>   References
>>   ==========
>>   
>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>> index a8efe1f6bf77..097bb2138360 100644
>> --- a/arch/x86/kvm/svm/sev.c
>> +++ b/arch/x86/kvm/svm/sev.c
>> @@ -22,6 +22,7 @@
>>   #include <asm/pkru.h>
>>   #include <asm/trapnr.h>
>>   #include <asm/fpu/xcr.h>
>> +#include <asm/sev.h>
>>   
>>   #include "mmu.h"
>>   #include "x86.h"
>> @@ -75,6 +76,8 @@ static unsigned int nr_asids;
>>   static unsigned long *sev_asid_bitmap;
>>   static unsigned long *sev_reclaim_asid_bitmap;
>>   
>> +static int snp_decommission_context(struct kvm *kvm);
>> +
>>   struct enc_region {
>>   	struct list_head list;
>>   	unsigned long npages;
>> @@ -100,12 +103,17 @@ static int sev_flush_asids(int min_asid, int max_asid)
>>   	down_write(&sev_deactivate_lock);
>>   
>>   	wbinvd_on_all_cpus();
>> -	ret = sev_guest_df_flush(&error);
>> +
>> +	if (sev_snp_enabled)
>> +		ret = sev_do_cmd(SEV_CMD_SNP_DF_FLUSH, NULL, &error);
>> +	else
>> +		ret = sev_guest_df_flush(&error);
>>   
>>   	up_write(&sev_deactivate_lock);
>>   
>>   	if (ret)
>> -		pr_err("SEV: DF_FLUSH failed, ret=%d, error=%#x\n", ret, error);
>> +		pr_err("SEV%s: DF_FLUSH failed, ret=%d, error=%#x\n",
>> +		       sev_snp_enabled ? "-SNP" : "", ret, error);
>>   
>>   	return ret;
>>   }
>> @@ -2011,6 +2019,80 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>>   	return ret;
>>   }
>>   
>> +/*
>> + * The guest context contains all the information, keys and metadata
>> + * associated with the guest that the firmware tracks to implement SEV
>> + * and SNP features. The firmware stores the guest context in hypervisor
>> + * provide page via the SNP_GCTX_CREATE command.
>> + */
>> +static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>> +{
>> +	struct sev_data_snp_addr data = {};
>> +	void *context;
>> +	int rc;
>> +
>> +	/* Allocate memory for context page */
>> +	context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
>> +	if (!context)
>> +		return NULL;
>> +
>> +	data.gctx_paddr = __psp_pa(context);
>> +	rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, &data, &argp->error);
>> +	if (rc) {
>> +		snp_free_firmware_page(context);
>> +		return NULL;
>> +	}
>> +
>> +	return context;
>> +}
>> +
>> +static int snp_bind_asid(struct kvm *kvm, int *error)
>> +{
>> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> +	struct sev_data_snp_activate data = {0};
>> +
>> +	data.gctx_paddr = __psp_pa(sev->snp_context);
>> +	data.asid   = sev_get_asid(kvm);
>> +	return sev_issue_cmd(kvm, SEV_CMD_SNP_ACTIVATE, &data, error);
> 
> According to the SNP ABI specification[1] 8.10 SNP_ACTIVATE:
> 
> "The firmware checks that a DF_FLUSH is not required. If a DF_FLUSH is
> required, the firmware returns DFFLUSH_REQUIRED. Note that all ASIDs are
> marked to require a DF_FLUSH at reset."
> 
> Do we need a SNP_DF_FLUSH here before calling SNP_ACTIVATE or handle the
> situation if the PSP firmware returns DFFLUSH_REQUIRED?
> 
> [1] https://www.amd.com/system/files/TechDocs/56860.pdf

This is related to ASID use. An initial DF_FLUSH is done which allows any 
SNP ASID to be used once without requiring a DF_FLUSH. Once an ASID has 
been used, it cannot be re-used until a DF_FLUSH is performed. The ASID 
recycling code takes care of that.

Thanks,
Tom

> 
>> +}
>> +
>> +static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>> +{
>> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> +	struct sev_data_snp_launch_start start = {0};
>> +	struct kvm_sev_snp_launch_start params;
>> +	int rc;
>> +
>> +	if (!sev_snp_guest(kvm))
>> +		return -ENOTTY;
>> +
>> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
>> +		return -EFAULT;
>> +
>> +	sev->snp_context = snp_context_create(kvm, argp);
>> +	if (!sev->snp_context)
>> +		return -ENOTTY;
>> +
>> +	start.gctx_paddr = __psp_pa(sev->snp_context);
>> +	start.policy = params.policy;
>> +	memcpy(start.gosvw, params.gosvw, sizeof(params.gosvw));
>> +	rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_START, &start, &argp->error);
>> +	if (rc)
>> +		goto e_free_context;
>> +
>> +	sev->fd = argp->sev_fd;
>> +	rc = snp_bind_asid(kvm, &argp->error);
>> +	if (rc)
>> +		goto e_free_context;
>> +
>> +	return 0;
>> +
>> +e_free_context:
>> +	snp_decommission_context(kvm);
>> +
>> +	return rc;
>> +}
>> +
>>   int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>>   {
>>   	struct kvm_sev_cmd sev_cmd;
>> @@ -2101,6 +2183,9 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>>   	case KVM_SEV_RECEIVE_FINISH:
>>   		r = sev_receive_finish(kvm, &sev_cmd);
>>   		break;
>> +	case KVM_SEV_SNP_LAUNCH_START:
>> +		r = snp_launch_start(kvm, &sev_cmd);
>> +		break;
>>   	default:
>>   		r = -EINVAL;
>>   		goto out;
>> @@ -2292,6 +2377,28 @@ int sev_vm_copy_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>>   	return ret;
>>   }
>>   
>> +static int snp_decommission_context(struct kvm *kvm)
>> +{
>> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> +	struct sev_data_snp_addr data = {};
>> +	int ret;
>> +
>> +	/* If context is not created then do nothing */
>> +	if (!sev->snp_context)
>> +		return 0;
>> +
>> +	data.gctx_paddr = __sme_pa(sev->snp_context);
>> +	ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
>> +	if (WARN_ONCE(ret, "failed to release guest context"))
>> +		return ret;
>> +
>> +	/* free the context page now */
>> +	snp_free_firmware_page(sev->snp_context);
>> +	sev->snp_context = NULL;
>> +
>> +	return 0;
>> +}
>> +
>>   void sev_vm_destroy(struct kvm *kvm)
>>   {
>>   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> @@ -2333,7 +2440,15 @@ void sev_vm_destroy(struct kvm *kvm)
>>   		}
>>   	}
>>   
>> -	sev_unbind_asid(kvm, sev->handle);
>> +	if (sev_snp_guest(kvm)) {
>> +		if (snp_decommission_context(kvm)) {
>> +			WARN_ONCE(1, "Failed to free SNP guest context, leaking asid!\n");
>> +			return;
>> +		}
>> +	} else {
>> +		sev_unbind_asid(kvm, sev->handle);
>> +	}
>> +
>>   	sev_asid_free(sev);
>>   }
>>   
>> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
>> index 56a5c96d8a36..740969b57425 100644
>> --- a/arch/x86/kvm/svm/svm.h
>> +++ b/arch/x86/kvm/svm/svm.h
>> @@ -92,6 +92,7 @@ struct kvm_sev_info {
>>   	struct misc_cg *misc_cg; /* For misc cgroup accounting */
>>   	atomic_t migration_in_progress;
>>   	u64 snp_init_flags;
>> +	void *snp_context;      /* SNP guest context page */
>>   };
>>   
>>   struct kvm_svm {
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 499cc323f793..cf19799ca5ce 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1919,6 +1919,7 @@ enum sev_cmd_id {
>>   
>>   	/* SNP specific commands */
>>   	KVM_SEV_SNP_INIT,
>> +	KVM_SEV_SNP_LAUNCH_START,
>>   
>>   	KVM_SEV_NR_MAX,
>>   };
>> @@ -2026,6 +2027,15 @@ struct kvm_snp_init {
>>   	__u64 flags;
>>   };
>>   
>> +struct kvm_sev_snp_launch_start {
>> +	__u64 policy;
>> +	__u64 ma_uaddr;
>> +	__u8 ma_en;
>> +	__u8 imi_en;
>> +	__u8 gosvw[16];
>> +	__u8 pad[6];
>> +};
>> +
>>   #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
>>   #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
>>   #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)
>