KVM: SVM: Add support for KVM_SEV_SEND_CANCEL command

After completion of SEND_START, but before SEND_FINISH, the source VMM can
issue the SEND_CANCEL command to stop a migration. This is necessary so
that a cancelled migration can restart with a new target later.

Reviewed-by: Nathan Tempelman <natet@google.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Steve Rutherford <srutherford@google.com>
Message-Id: <20210412194408.2458827-1-srutherford@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/amd-memory-encryption.rst

@@ -356,6 +356,15 @@ issued by the hypervisor to delete the encryption context.
 
 Returns: 0 on success, -negative on error
 
+14. KVM_SEV_SEND_CANCEL
+------------------------
+
+After completion of SEND_START, but before SEND_FINISH, the source VMM can issue the
+SEND_CANCEL command to stop a migration. This is necessary so that a cancelled
+migration can restart with a new target later.
+
+Returns: 0 on success, -negative on error
+
 References
 ==========
 

arch/x86/kvm/svm/sev.c

@@ -1377,6 +1377,26 @@ static int sev_send_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int sev_send_cancel(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_send_cancel *data;
+	int ret;
+
+	if (!sev_guest(kvm))
+		return -ENOTTY;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->handle = sev->handle;
+	ret = sev_issue_cmd(kvm, SEV_CMD_SEND_CANCEL, data, &argp->error);
+
+	kfree(data);
+	return ret;
+}
+
 int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -1448,6 +1468,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_SEND_FINISH:
 		r = sev_send_finish(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_SEND_CANCEL:
+		r = sev_send_cancel(kvm, &sev_cmd);
+		break;
 	default:
 		r = -EINVAL;
 		goto out;

drivers/crypto/ccp/sev-dev.c

@@ -129,6 +129,7 @@ static int sev_cmd_buffer_len(int cmd)
 	case SEV_CMD_DOWNLOAD_FIRMWARE:		return sizeof(struct sev_data_download_firmware);
 	case SEV_CMD_GET_ID:			return sizeof(struct sev_data_get_id);
 	case SEV_CMD_ATTESTATION_REPORT:	return sizeof(struct sev_data_attestation_report);
+	case SEV_CMD_SEND_CANCEL:			return sizeof(struct sev_data_send_cancel);
 	default:				return 0;
 	}
 

include/linux/psp-sev.h

@@ -73,6 +73,7 @@ enum sev_cmd {
 	SEV_CMD_SEND_UPDATE_DATA	= 0x041,
 	SEV_CMD_SEND_UPDATE_VMSA	= 0x042,
 	SEV_CMD_SEND_FINISH		= 0x043,
+	SEV_CMD_SEND_CANCEL		= 0x044,
 
 	/* Guest migration commands (incoming) */
 	SEV_CMD_RECEIVE_START		= 0x050,
@@ -392,6 +393,15 @@ struct sev_data_send_finish {
 	u32 handle;				/* In */
 } __packed;
 
+/**
+ * struct sev_data_send_cancel - SEND_CANCEL command parameters
+ *
+ * @handle: handle of the VM to process
+ */
+struct sev_data_send_cancel {
+	u32 handle;				/* In */
+} __packed;
+
 /**
  * struct sev_data_receive_start - RECEIVE_START command parameters
  *

include/uapi/linux/kvm.h

@@ -1674,6 +1674,8 @@ enum sev_cmd_id {
 	KVM_SEV_CERT_EXPORT,
 	/* Attestation report */
 	KVM_SEV_GET_ATTESTATION_REPORT,
+	/* Guest Migration Extension */
+	KVM_SEV_SEND_CANCEL,
 
 	KVM_SEV_NR_MAX,
 };