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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Singh, Brijesh (brijesh.singh@amd.com) wrote:
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  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
            ^an outgoing                                       ^ d*i*ctates

> +the certificate passed through the migrate-sev-set-info command will be
> +validate. SEND_UPDATE_DATA is called to encrypt the guest private pages.
          ^ validate*d* ?  How does the cert get validated anyway? As a
guest owner what rules can I set about which other host it gets migrated
to?

Actually, thinking about it, I didn't notice anything in the patchset
that checked/gave diagnostics about the guest policy - shouldn't there
be something that nicely says something like:
  'Guest policy has NOSEND set, guest can not be migrated'

?

> +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.
                                                              ^ 'the' not needed
> +
> +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
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK