[Qemu-devel] [PATCH v2 06/13] doc: update AMD SEV to include Live migration flow

[Singh, Brijesh]

Signed-off-by: Brijesh Singh <address@hidden>
---
 docs/amd-memory-encryption.txt | 42 +++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt
index abb9a976f5..374f4b0a94 100644
--- a/docs/amd-memory-encryption.txt
+++ b/docs/amd-memory-encryption.txt
@@ -89,7 +89,47 @@ TODO
 
 Live Migration
 ----------------
-TODO
+AMD SEV encrypts the memory of VMs and because a different key is used
+in each VM, the hypervisor will be unable to simply copy the
+ciphertext from one VM to another to migrate the VM. Instead the AMD SEV Key
+Management API provides sets of function which the hypervisor can use
+to package a guest page for migration, while maintaining the confidentiality
+provided by AMD SEV.
+
+SEV guest VMs have the concept of private and shared memory. The private
+memory is encrypted with the guest-specific key, while shared memory may
+be encrypted with the hypervisor key. The migration APIs provided by the
+SEV API spec should be used for migrating the private pages. The
+KVM_GET_PAGE_ENC_BITMAP ioctl can be used to get the guest page encryption
+bitmap. The bitmap can be used to check if the given guest page is
+private or shared.
+
+Before initiating the migration, we need to know the targets machine's public
+Diffie-Hellman key (PDH) and certificate chain. It can be retrieved
+with the 'query-sev-capabilities' QMP command or using the sev-tool. The
+migrate-set-sev-info object can be used to pass the target machine's PDH and
+certificate chain.
+
+e.g
+(QMP) migrate-sev-set-info pdh=<target_pdh> plat-cert=<target_cert_chain> \
+       amd-cert=<amd_cert>
+(QMP) migrate tcp:0:4444
+
+
+During the migration flow, the SEND_START is called on the source hypervisor
+to create outgoing encryption context. The SEV guest policy dectates whether
+the certificate passed through the migrate-sev-set-info command will be
+validate. SEND_UPDATE_DATA is called to encrypt the guest private pages.
+After migration is completed, SEND_FINISH is called to destroy the encryption
+context and make the VM non-runnable to protect it against the cloning.
+
+On the target machine, RECEIVE_START is called first to create an
+incoming encryption context. The RECEIVE_UPDATE_DATA is called to copy
+the receieved encrypted page into guest memory. After migration has
+completed, RECEIVE_FINISH is called to make the VM runnable.
+
+For more information about the migration see SEV API Appendix A
+Usage flow (Live migration section).
 
 References
 -----------------
-- 
2.17.1