Re: [PATCH RFC v8 45/56] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event

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

On Mon, 20 Feb 2023 12:38:36 -0600
Michael Roth <michael.roth@amd.com> wrote:

> From: Brijesh Singh <brijesh.singh@amd.com>
> 
> Version 2 of GHCB specification added the support for two SNP Guest
> Request Message NAE events. The events allows for an SEV-SNP guest to
> make request to the SEV-SNP firmware through hypervisor using the
> SNP_GUEST_REQUEST API define in the SEV-SNP firmware specification.
> 
> The SNP_EXT_GUEST_REQUEST is similar to SNP_GUEST_REQUEST with the
> difference of an additional certificate blob that can be passed through
> the SNP_SET_CONFIG ioctl defined in the CCP driver. The CCP driver
> provides snp_guest_ext_guest_request() that is used by the KVM to get
> both the report and certificate data at once.
> 
> 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>
> ---
>  arch/x86/kvm/svm/sev.c | 185 +++++++++++++++++++++++++++++++++++++++--
>  arch/x86/kvm/svm/svm.h |   2 +
>  2 files changed, 181 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 197b1f904567..92179614102e 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -327,6 +327,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		if (ret)
>  			goto e_free;
>  
> +		mutex_init(&sev->guest_req_lock);
>  		ret = sev_snp_init(&argp->error, false);
>  	} else {
>  		ret = sev_platform_init(&argp->error);
> @@ -2059,23 +2060,34 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
>   */
>  static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  {
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>  	struct sev_data_snp_addr data = {};
> -	void *context;
> +	void *context, *certs_data;
>  	int rc;
>  
> +	/* Allocate memory used for the certs data in SNP guest request */
> +	certs_data = kzalloc(SEV_FW_BLOB_MAX_SIZE, GFP_KERNEL_ACCOUNT);
> +	if (!certs_data)
> +		return NULL;
> +
>  	/* Allocate memory for context page */
>  	context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
>  	if (!context)
> -		return NULL;
> +		goto e_free;
>  
>  	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;
> -	}
> +	if (rc)
> +		goto e_free;
> +
> +	sev->snp_certs_data = certs_data;
>  
>  	return context;
> +
> +e_free:
> +	snp_free_firmware_page(context);
> +	kfree(certs_data);
> +	return NULL;
>  }
>  
>  static int snp_bind_asid(struct kvm *kvm, int *error)
> @@ -2693,6 +2705,8 @@ static int snp_decommission_context(struct kvm *kvm)
>  	snp_free_firmware_page(sev->snp_context);
>  	sev->snp_context = NULL;
>  
> +	kfree(sev->snp_certs_data);
> +
>  	return 0;
>  }
>  
> @@ -3153,6 +3167,8 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
>  	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>  	case SVM_VMGEXIT_HV_FEATURES:
>  	case SVM_VMGEXIT_PSC:
> +	case SVM_VMGEXIT_GUEST_REQUEST:
> +	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
>  		break;
>  	default:
>  		reason = GHCB_ERR_INVALID_EVENT;
> @@ -3384,6 +3400,149 @@ static int snp_complete_psc(struct kvm_vcpu *vcpu)
>  	return 1;
>  }
>  
> +static unsigned long snp_setup_guest_buf(struct vcpu_svm *svm,
> +					 struct sev_data_snp_guest_request *data,
> +					 gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	kvm_pfn_t req_pfn, resp_pfn;
> +	struct kvm_sev_info *sev;
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	if (!IS_ALIGNED(req_gpa, PAGE_SIZE) || !IS_ALIGNED(resp_gpa, PAGE_SIZE))
> +		return SEV_RET_INVALID_PARAM;
> +
> +	req_pfn = gfn_to_pfn(kvm, gpa_to_gfn(req_gpa));
> +	if (is_error_noslot_pfn(req_pfn))
> +		return SEV_RET_INVALID_ADDRESS;
> +
> +	resp_pfn = gfn_to_pfn(kvm, gpa_to_gfn(resp_gpa));
> +	if (is_error_noslot_pfn(resp_pfn))
> +		return SEV_RET_INVALID_ADDRESS;
> +
> +	if (rmp_make_private(resp_pfn, 0, PG_LEVEL_4K, 0, true))
> +		return SEV_RET_INVALID_ADDRESS;
> +
> +	data->gctx_paddr = __psp_pa(sev->snp_context);
> +	data->req_paddr = __sme_set(req_pfn << PAGE_SHIFT);
> +	data->res_paddr = __sme_set(resp_pfn << PAGE_SHIFT);
> +
> +	return 0;
> +}
> +
> +static void snp_cleanup_guest_buf(struct sev_data_snp_guest_request *data, unsigned long *rc)
> +{
> +	u64 pfn = __sme_clr(data->res_paddr) >> PAGE_SHIFT;
> +	int ret;
> +
> +	ret = snp_page_reclaim(pfn);
> +	if (ret)
> +		*rc = SEV_RET_INVALID_ADDRESS;
> +
> +	ret = rmp_make_shared(pfn, PG_LEVEL_4K);
> +	if (ret)
> +		*rc = SEV_RET_INVALID_ADDRESS;
> +}
> +
> +static void snp_handle_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct sev_data_snp_guest_request data = {0};
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_sev_info *sev;
> +	unsigned long rc;
> +	int err;
> +
> +	if (!sev_snp_guest(vcpu->kvm)) {
> +		rc = SEV_RET_INVALID_GUEST;
> +		goto e_fail;
> +	}
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	mutex_lock(&sev->guest_req_lock);
> +
> +	rc = snp_setup_guest_buf(svm, &data, req_gpa, resp_gpa);
> +	if (rc)
> +		goto unlock;
> +
> +	rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data, &err);
> +	if (rc)
> +		/* use the firmware error code */
> +		rc = err;
> +
> +	snp_cleanup_guest_buf(&data, &rc);
> +

I am curious about the reason of having a shared-private and private-shared
conversion before and after issuing the command to firmware.

Is it because the firmware requires the resp page has to be a private page?
while the req page is not. (I understand that the req/resp page should be
shared before returnning to guest due to GHCB spec)

> +unlock:
> +	mutex_unlock(&sev->guest_req_lock);
> +
> +e_fail:
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, rc);
> +}
> +
> +static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct sev_data_snp_guest_request req = {0};
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	unsigned long data_npages;
> +	struct kvm_sev_info *sev;
> +	unsigned long rc, err;
> +	u64 data_gpa;
> +
> +	if (!sev_snp_guest(vcpu->kvm)) {
> +		rc = SEV_RET_INVALID_GUEST;
> +		goto e_fail;
> +	}
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
> +	data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
> +
> +	if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) {
> +		rc = SEV_RET_INVALID_ADDRESS;
> +		goto e_fail;
> +	}
> +
> +	mutex_lock(&sev->guest_req_lock);
> +
> +	rc = snp_setup_guest_buf(svm, &req, req_gpa, resp_gpa);
> +	if (rc)
> +		goto unlock;
> +
> +	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
> +					 &data_npages, &err);
> +	if (rc) {
> +		/*
> +		 * If buffer length is small then return the expected
> +		 * length in rbx.
> +		 */
> +		if (err == SNP_GUEST_REQ_INVALID_LEN)
> +			vcpu->arch.regs[VCPU_REGS_RBX] = data_npages;
> +
> +		/* pass the firmware error code */
> +		rc = err;
> +		goto cleanup;
> +	}
> +
> +	/* Copy the certificate blob in the guest memory */
> +	if (data_npages &&
> +	    kvm_write_guest(kvm, data_gpa, sev->snp_certs_data, data_npages << PAGE_SHIFT))
> +		rc = SEV_RET_INVALID_ADDRESS;
> +
> +cleanup:
> +	snp_cleanup_guest_buf(&req, &rc);
> +
> +unlock:
> +	mutex_unlock(&sev->guest_req_lock);
> +
> +e_fail:
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, rc);
> +}
> +
>  static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
>  {
>  	struct vmcb_control_area *control = &svm->vmcb->control;
> @@ -3633,6 +3792,20 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
>  		vcpu->run->vmgexit.ghcb_msr = ghcb_gpa;
>  		vcpu->arch.complete_userspace_io = snp_complete_psc;
>  		break;
> +	case SVM_VMGEXIT_GUEST_REQUEST: {
> +		snp_handle_guest_request(svm, control->exit_info_1, control->exit_info_2);
> +
> +		ret = 1;
> +		break;
> +	}
> +	case SVM_VMGEXIT_EXT_GUEST_REQUEST: {
> +		snp_handle_ext_guest_request(svm,
> +					     control->exit_info_1,
> +					     control->exit_info_2);
> +
> +		ret = 1;
> +		break;
> +	}
>  	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>  		vcpu_unimpl(vcpu,
>  			    "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 13b00233b315..4a9ffb7e5139 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -93,6 +93,8 @@ struct kvm_sev_info {
>  	atomic_t migration_in_progress;
>  	u64 snp_init_flags;
>  	void *snp_context;      /* SNP guest context page */
> +	void *snp_certs_data;
> +	struct mutex guest_req_lock; /* Lock for guest request handling */
>  };
>  
>  struct kvm_svm {