KVM: SVM: Add KVM_SEV SEND_START command

The command is used to create an outgoing SEV guest encryption context.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Steve Rutherford <srutherford@google.com>
Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Message-Id: <2f1686d0164e0f1b3d6a41d620408393e0a48376.1618498113.git.ashish.kalra@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -290,6 +290,36 @@ Returns: 0 on success, -negative on error
                 __u32 len;
         };
 
+11. KVM_SEV_SEND_START
+----------------------
+
+The KVM_SEV_SEND_START command can be used by the hypervisor to create an
+outgoing guest encryption context.
+
+If session_len is zero on entry, the length of the guest session information is
+written to session_len and all other fields are not used.
+
+Parameters (in): struct kvm_sev_send_start
+
+Returns: 0 on success, -negative on error
+
+::
+        struct kvm_sev_send_start {
+                __u32 policy;                 /* guest policy */
+
+                __u64 pdh_cert_uaddr;         /* platform Diffie-Hellman certificate */
+                __u32 pdh_cert_len;
+
+                __u64 plat_certs_uaddr;        /* platform certificate chain */
+                __u32 plat_certs_len;
+
+                __u64 amd_certs_uaddr;        /* AMD certificate */
+                __u32 amd_certs_len;
+
+                __u64 session_uaddr;          /* Guest session information */
+                __u32 session_len;
+        };
+
 References
 ==========