Dne 04. 03. 20 v 18:27 Igor Mammedov napsal(a): > Migration from QEMU(v4.0) fails when using 3.1 or older machine > type. For example if one attempts to migrate > QEMU-2.12 started as > qemu-system-ppc64 -nodefaults -M pseries-2.12 -m 4096 -mem-path /tmp/ > to current master, it will fail with > qemu-system-ppc64: Unknown ramblock "ppc_spapr.ram", cannot accept migration > qemu-system-ppc64: error while loading state for instance 0x0 of device > 'ram' > qemu-system-ppc64: load of migration failed: Invalid argument > > Caused by 900c0ba373 commit which switches main RAM allocation to > memory backends and the fact in 3.1 and older QEMU, backends used > full[***] QOM path as memory region name instead of backend's name. > That was changed after 3.1 to use prefix-less names by default > (fa0cb34d22) for new machine types. > *** effectively makes main RAM memory region names defined by > MachineClass::default_ram_id being altered with '/objects/' prefix > and therefore migration fails as old QEMU sends prefix-less > name while new QEMU expects name with prefix when using 3.1 and > older machine types. > > Fix it by forcing implicit[1] memory backend to always use > prefix-less names for its memory region by setting > 'x-use-canonical-path-for-ramblock-id' > property to false. > > 1) i.e. memory backend created by compat glue which maps > -m/-mem-path/-mem-prealloc/default RAM size into > appropriate backend type/options to match old CLI format. > > Fixes: 900c0ba373 > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > Reported-by: Lukáš Doktor <ldok...@redhat.com> > --- > CC: ldok...@redhat.com > CC: marcandre.lur...@redhat.com > CC: dgilb...@redhat.com > --- > softmmu/vl.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/softmmu/vl.c b/softmmu/vl.c > index 5549f4b619..1101b1cb41 100644 > --- a/softmmu/vl.c > +++ b/softmmu/vl.c > @@ -2800,6 +2800,9 @@ static void create_default_memdev(MachineState *ms, > const char *path) > object_property_set_int(obj, ms->ram_size, "size", &error_fatal); > object_property_add_child(object_get_objects_root(), mc->default_ram_id, > obj, &error_fatal); > + /* Ensure backend's memory region name is equal to mc->default_ram_id */ > + object_property_set_bool(obj, false, > "x-use-canonical-path-for-ramblock-id", > + &error_fatal); > user_creatable_complete(USER_CREATABLE(obj), &error_fatal); > object_unref(obj); > object_property_set_str(OBJECT(ms), mc->default_ram_id, "memory-backend", >
Tested-by: Lukáš Doktor <ldok...@redhat.com> I can't say anything about the code, but functional-wise it addresses the issue and fixes post_copy hugepages migration in my mini-CI (variants 2.10, 2.12, 3.0, 3.1, 4.0 -> master and vice-versa are failing with master and passing with this patch). Regards, Lukáš
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