KVM: Introduce KVM_MEMORY_ENCRYPT_OP ioctl

If the hardware supports memory encryption then the
KVM_MEMORY_ENCRYPT_OP ioctl can be used by qemu to issue a platform
specific memory encryption commands.

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: "Radim Krčmář" <rkrcmar@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
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Borislav Petkov <bp@suse.de>

Documentation/virtual/kvm/api.txt

@@ -3394,6 +3394,22 @@ invalid, if invalid pages are written to (e.g. after the end of memory)
 or if no page table is present for the addresses (e.g. when using
 hugepages).
 
+4.109 KVM_MEMORY_ENCRYPT_OP
+
+Capability: basic
+Architectures: x86
+Type: system
+Parameters: an opaque platform specific structure (in/out)
+Returns: 0 on success; -1 on error
+
+If the platform supports creating encrypted VMs then this ioctl can be used
+for issuing platform-specific memory encryption commands to manage those
+encrypted VMs.
+
+Currently, this ioctl is used for issuing Secure Encrypted Virtualization
+(SEV) commands on AMD Processors. The SEV commands are defined in
+Documentation/virtual/kvm/amd-memory-encryption.txt.
+
 5. The kvm_run structure
 ------------------------