Re: [PATCH v13 09/26] KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command

[Sean Christopherson]

On Thu, Apr 18, 2024, Michael Roth wrote:
> +static inline bool sev_version_greater_or_equal(u8 major, u8 minor)
> +{
> +	if (major < SNP_POLICY_API_MAJOR)
> +		return true;
> +
> +	if (major == SNP_POLICY_API_MAJOR && minor <= SNP_POLICY_API_MINOR)
> +		return true;
> +
> +	return false;
> +}
> +
> +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;
> +	u8 major, minor;
> +	int rc;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (copy_from_user(&params, u64_to_user_ptr(argp->data), sizeof(params)))
> +		return -EFAULT;
> +
> +	/* Don't allow userspace to allocate memory for more than 1 SNP context. */
> +	if (sev->snp_context) {
> +		pr_debug("SEV-SNP context already exists. Refusing to allocate an additional one.\n");

What's the plan with all these printks?   There are far too many in this series.
Some might be useful, but many of them have no business landing upstream.

> +		return -EINVAL;
> +	}
> +
> +	sev->snp_context = snp_context_create(kvm, argp);
> +	if (!sev->snp_context)
> +		return -ENOTTY;
> +
> +	if (params.policy & ~SNP_POLICY_MASK_VALID) {
> +		pr_debug("SEV-SNP hypervisor does not support requested policy %llx (supported %llx).\n",

What does "SEV-SNP hypervisor" even mean?

> +			 params.policy, SNP_POLICY_MASK_VALID);
> +		return -EINVAL;
> +	}
> +
> +	if (!(params.policy & SNP_POLICY_MASK_RSVD_MBO)) {
> +		pr_debug("SEV-SNP hypervisor does not support requested policy %llx (must be set %llx).\n",
> +			 params.policy, SNP_POLICY_MASK_RSVD_MBO);
> +		return -EINVAL;
> +	}
> +
> +	if (params.policy & SNP_POLICY_MASK_SINGLE_SOCKET) {
> +		pr_debug("SEV-SNP hypervisor does not support limiting guests to a single socket.\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!(params.policy & SNP_POLICY_MASK_SMT)) {
> +		pr_debug("SEV-SNP hypervisor does not support limiting guests to a single SMT thread.\n");
> +		return -EINVAL;
> +	}
> +
> +	major = (params.policy & SNP_POLICY_MASK_API_MAJOR);
> +	minor = (params.policy & SNP_POLICY_MASK_API_MINOR);
> +	if (!sev_version_greater_or_equal(major, minor)) {

Why does this need a someone weirdly named helper?  Isn't this just?

	if (major < SNP_POLICY_API_MAJOR ||
	    (major == SNP_POLICY_API_MAJOR && minor < SNP_POLICY_API_MINOR))

> +		pr_debug("SEV-SNP hypervisor does not support requested version %d.%d (have %d,%d).\n",
> +			 major, minor, SNP_POLICY_API_MAJOR, SNP_POLICY_API_MINOR);
> +		return -EINVAL;
> +	}
> +
> +	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) {
> +		pr_debug("SEV_CMD_SNP_LAUNCH_START firmware command failed, rc %d\n", rc);
> +		goto e_free_context;
> +	}
> +
> +	sev->fd = argp->sev_fd;
> +	rc = snp_bind_asid(kvm, &argp->error);
> +	if (rc) {
> +		pr_debug("Failed to bind ASID to SEV-SNP context, rc %d\n", 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;
> @@ -1999,6 +2154,15 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  		goto out;
>  	}
>  
> +	/*
> +	 * Once KVM_SEV_INIT2 initializes a KVM instance as an SNP guest, only
> +	 * allow the use of SNP-specific commands.
> +	 */
> +	if (sev_snp_guest(kvm) && sev_cmd.id < KVM_SEV_SNP_LAUNCH_START) {
> +		r = -EPERM;
> +		goto out;
> +	}
> +
>  	switch (sev_cmd.id) {
>  	case KVM_SEV_ES_INIT:
>  		if (!sev_es_enabled) {
> @@ -2063,6 +2227,9 @@ 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;
> @@ -2258,6 +2425,33 @@ 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.address = __sme_pa(sev->snp_context);
> +	down_write(&sev_deactivate_lock);
> +	ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
> +	if (WARN_ONCE(ret, "failed to release guest context")) {

WARN here, or WARN in the caller, not both.  And if you warn here, this can be

	down_write(&sev_deactivate_lock);
	ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
	up_write(&sev_deactivate_lock);

	if (WARN_ONCE(ret, "..."))

> +		up_write(&sev_deactivate_lock);
> +		return ret;
> +	}
> +
> +	up_write(&sev_deactivate_lock);
> +
> +	/* free the context page now */

This doesn't seem like a particularly useful comment.  What would be useful is
a comment explaining the "decommission" unbinds the ASID.  

> +	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;
> @@ -2299,7 +2493,15 @@ 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");

WARN on the actually failure, not '1'.  And a newline isn't needed.

		if (WARN_ONCE(snp_decommission_context(kvm)
			      "Failed to free SNP guest context, leaking asid!"))
			return;

> +			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 7f2e9c7fc4ca..0654fc91d4db 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -92,6 +92,7 @@ struct kvm_sev_info {
>  	struct list_head mirror_entry; /* Use as a list entry of mirrors */
>  	struct misc_cg *misc_cg; /* For misc cgroup accounting */
>  	atomic_t migration_in_progress;
> +	void *snp_context;      /* SNP guest context page */
>  };
>  
>  struct kvm_svm {
> -- 
> 2.25.1
>