Hi Fabiano,
On 9/1/24 21:21, Fabiano Rosas wrote:
Cédric Le Goater <c...@kaod.org> writes:
On 1/9/24 18:40, Fabiano Rosas wrote:
Cédric Le Goater <c...@kaod.org> writes:
On 1/3/24 20:53, Fabiano Rosas wrote:
Philippe Mathieu-Daudé <phi...@linaro.org> writes:
+Peter/Fabiano
On 2/1/24 17:41, Cédric Le Goater wrote:
On 1/2/24 17:15, Philippe Mathieu-Daudé wrote:
Hi Cédric,
On 2/1/24 15:55, Cédric Le Goater wrote:
On 12/12/23 17:29, Philippe Mathieu-Daudé wrote:
Hi,
When a MPCore cluster is used, the Cortex-A cores belong the the
cluster container, not to the board/soc layer. This series move
the creation of vCPUs to the MPCore private container.
Doing so we consolidate the QOM model, moving common code in a
central place (abstract MPCore parent).
Changing the QOM hierarchy has an impact on the state of the machine
and some fixups are then required to maintain migration compatibility.
This can become a real headache for KVM machines like virt for which
migration compatibility is a feature, less for emulated ones.
All changes are either moving properties (which are not migrated)
or moving non-migrated QOM members (i.e. pointers of ARMCPU, which
is still migrated elsewhere). So I don't see any obvious migration
problem, but I might be missing something, so I Cc'ed Juan :>
FWIW, I didn't spot anything problematic either.
I've ran this through my migration compatibility series [1] and it
doesn't regress aarch64 migration from/to 8.2. The tests use '-M
virt -cpu max', so the cortex-a7 and cortex-a15 are not covered. I don't
think we even support migration of anything non-KVM on arm.
it happens we do.
Oh, sorry, I didn't mean TCG here. Probably meant to say something like
non-KVM-capable cpus, as in 32-bit. Nevermind.
Theoretically, we should be able to migrate to a TCG guest. Well, this
worked in the past for PPC. When I was doing more KVM related changes,
this was very useful for dev. Also, some machines are partially emulated.
Anyhow I agree this is not a strong requirement and we often break it.
Let's focus on KVM only.
1- https://gitlab.com/farosas/qemu/-/jobs/5853599533
yes it depends on the QOM hierarchy and virt seems immune to the changes.
Good.
However, changing the QOM topology clearly breaks migration compat,
Well, "clearly" is relative =) You've mentioned pseries and aspeed
already, do you have a pointer to one of those cases were we broke
migration
Regarding pseries, migration compat broke because of 5bc8d26de20c
("spapr: allocate the ICPState object from under sPAPRCPUCore") which
is similar to the changes proposed by this series, it impacts the QOM
hierarchy. Here is the workaround/fix from Greg : 46f7afa37096
("spapr: fix migration of ICPState objects from/to older QEMU") which
is quite an headache and this turned out to raise another problem some
months ago ... :/ That's why I sent [1] to prepare removal of old
machines and workarounds becoming a burden.
This feels like something that could be handled by the vmstate code
somehow. The state is there, just under a different path.
What, the QOM path is used in migration? ...
See recent discussions on "QOM path stability":
https://lore.kernel.org/qemu-devel/zzfyvlmcxbcia...@redhat.com/
https://lore.kernel.org/qemu-devel/87jzojbxt7....@pond.sub.org/
https://lore.kernel.org/qemu-devel/87v883by34....@pond.sub.org/
No one wants
to be policing QOM hierarchy changes in every single series that shows
up on the list.
Anyway, thanks for the pointers. I'll study that code a bit more, maybe
I can come up with some way to handle these cases.
Hopefully between the analyze-migration test and the compat tests we'll
catch the next bug of this kind before it gets merged.
