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

[Zhi Wang <zhi.wang.linux@gmail.com>]

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

> +}
> +
> +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)