These two independent bugs both sit on the libvhost-user postcopy path and together make postcopy migration of a guest with a libvhost-user backend fail. They are only reachable when the backend negotiates VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS, i.e. it adds memory regions one by one with VHOST_USER_ADD_MEM_REG instead of VHOST_USER_SET_MEM_TABLE.
Patch 1 stops the backend from panicking on the "all postcopy client bases received" ack, which QEMU sends as an fd-less VHOST_USER_ADD_MEM_REG. Patch 2 makes the backend return its mapping address for a region added that way, without which QEMU cannot translate the backend's fault addresses back to a RAMBlock. Reproduced and fixed with contrib/vhost-user-bridge as the net backend of a postcopy migrated guest: before the series the destination backend either panics or QEMU reports "Failed to find region for fault"; after it the migration completes. Bin Guo (2): libvhost-user: accept the postcopy client base ack in vu_add_mem_reg() libvhost-user: return the backend mapping address for added regions subprojects/libvhost-user/libvhost-user.c | 34 ++++++++++++++--------- 1 file changed, 21 insertions(+), 13 deletions(-) -- 2.50.1 (Apple Git-155)
