Memory: Only call ramblock_ptr when needed in qemu_ram_writeback
It is possible that a ramblock doesn't have memory that QEMU can
access, this is the case with the Xen hypervisor.
In order to avoid to trigger an assert, only call ramblock_ptr() when
needed in qemu_ram_writeback(). This should fix migration of Xen
guests that was broken with
bd108a44bc29 ("migration: ram: Switch to
ram block writeback").
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <
20191219154323.325255-1-anthony.perard@citrix.com>