From a3eae205c601dd491d2e83fa9ff0d15fce7236b5 Mon Sep 17 00:00:00 2001 From: Steve Sistare Date: Wed, 1 Oct 2025 08:33:58 -0700 Subject: migration: cpr-exec mode Add the cpr-exec migration mode. Usage: qemu-system-$arch -machine aux-ram-share=on ... migrate_set_parameter mode cpr-exec migrate_set_parameter cpr-exec-command \ ... -incoming \ migrate -d The migrate command stops the VM, saves state to uri-1, directly exec's a new version of QEMU on the same host, replacing the original process while retaining its PID, and loads state from uri-1. Guest RAM is preserved in place, albeit with new virtual addresses. The new QEMU process is started by exec'ing the command specified by the @cpr-exec-command parameter. The first word of the command is the binary, and the remaining words are its arguments. The command may be a direct invocation of new QEMU, or may be a non-QEMU command that exec's the new QEMU binary. This mode creates a second migration channel that is not visible to the user. At the start of migration, old QEMU saves CPR state to the second channel, and at the end of migration, it tells the main loop to call cpr_exec. New QEMU loads CPR state early, before objects are created. Because old QEMU terminates when new QEMU starts, one cannot stream data between the two, so uri-1 must be a type, such as a file, that accepts all data before old QEMU exits. Otherwise, old QEMU may quietly block writing to the channel. Memory-backend objects must have the share=on attribute, but memory-backend-epc is not supported. The VM must be started with the '-machine aux-ram-share=on' option, which allows anonymous memory to be transferred in place to the new process. The memfds are kept open across exec by clearing the close-on-exec flag, their values are saved in CPR state, and they are mmap'd in new QEMU. Signed-off-by: Steve Sistare Acked-by: Markus Armbruster Link: https://lore.kernel.org/r/1759332851-370353-7-git-send-email-steven.sistare@oracle.com Signed-off-by: Peter Xu --- migration/ram.c | 1 + 1 file changed, 1 insertion(+) (limited to 'migration/ram.c') diff --git a/migration/ram.c b/migration/ram.c index a8e8d2cc67..9aac89638a 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -228,6 +228,7 @@ bool migrate_ram_is_ignored(RAMBlock *block) MigMode mode = migrate_mode(); return !qemu_ram_is_migratable(block) || mode == MIG_MODE_CPR_TRANSFER || + mode == MIG_MODE_CPR_EXEC || (migrate_ignore_shared() && qemu_ram_is_shared(block) && qemu_ram_is_named_file(block)); } -- cgit 1.4.1