fridtjof/qemu-cr16
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

migration/postcopy: Initialize blocktime context only until listen

Browse source 
Before this patch, the blocktime context can be created very early, because
postcopy_ram_supported_by_host() <- migrate_caps_check() can happen during
migration object init.

The trick here is the blocktime context needs system vCPU information,
which seems to be possible to change after that point.  I didn't verify it,
but it doesn't sound right.

Now move it out and initialize the context only when postcopy listen
starts.  That is already during a migration so it should be guaranteed the
vCPU topology can never change on both sides.

While at it, assert that the ctx isn't created instead this time; the old
"if" trick isn't needed when we're sure it will only happen once now.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20250613141217.474825-10-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
This commit is contained in:
Peter Xu 2025-06-13 10:12:12 -04:00 • committed by Fabiano Rosas
parent b4c82b4288
commit f07f2a3092
1 changed files with 10 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

15
migration/postcopy-ram.c
View file

@ -325,13 +325,13 @@ static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis,
}
#ifdef UFFD_FEATURE_THREAD_ID
/*
* Postcopy blocktime conditionally needs THREAD_ID feature (introduced
* to Linux in 2017). Always try to enable it when QEMU is compiled
* with such environment.
*/
if (UFFD_FEATURE_THREAD_ID & supported_features) {
asked_features |= UFFD_FEATURE_THREAD_ID;
if (migrate_postcopy_blocktime()) {
if (!mis->blocktime_ctx) {
mis->blocktime_ctx = blocktime_context_new();
}
}
}
#endif
@ -1239,6 +1239,11 @@ int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
return -1;
}
if (migrate_postcopy_blocktime()) {
assert(mis->blocktime_ctx == NULL);
mis->blocktime_ctx = blocktime_context_new();
}
/* Now an eventfd we use to tell the fault-thread to quit */
mis->userfault_event_fd = eventfd(0, EFD_CLOEXEC);
if (mis->userfault_event_fd == -1) {