Re: [PATCH v2 01/18] aspeed/smc: Fix write incorrect data into flash in user mode

[Kevin Wolf <kwolf@redhat.com>]

Am 22.10.2024 um 15:40 hat Cédric Le Goater geschrieben:
> > >   static const VMStateDescription vmstate_aspeed_smc = {
> > >       .name = "aspeed.smc",
> > > -    .version_id = 2,
> > > +    .version_id = 3,
> > >       .minimum_version_id = 2,
> > >       .fields = (const VMStateField[]) {
> > >           VMSTATE_UINT32_ARRAY(regs, AspeedSMCState, ASPEED_SMC_R_MAX),
> > >           VMSTATE_UINT8(snoop_index, AspeedSMCState),
> > >           VMSTATE_UINT8(snoop_dummies, AspeedSMCState),
> > > +        VMSTATE_BOOL(unselect, AspeedSMCState),
> > >           VMSTATE_END_OF_LIST()
> > >       }
> > >   };
> > 
> > I think this will break migration compatibility. In order to enable
> > at least forward migration, it should be:
> > 
> >      VMSTATE_BOOL_V(unselect, AspeedSMCState, 3),
> 
> This is correct. I will fix the patch.
> 
> Some background,
> 
> The aspeed machines are fully emulated and the Aspeed SoC models are not
> part of any virt* machines (yet). So migration support is a bit of a
> theory. We have done our best to maintain some support, compatibility
> not being a priority. IOW, it's not perfectly tuned as on virt machines.
> 
> Also, on ARM, migration of the CPU secure mode (I think this is the reason,
> Peter please correct me !) is not supported and if migration is initiated
> after Linux has started, the machine will hang.

That's a good reason not to implement backwards migration for now, it
would only complicate things. But as long as we claim to be migratable
by having VMStateDescriptions and even increasing version_id, we should
at least try to keep that part correct.

> However, if one day, an aspeed model becomes part of a virt machine, we
> should be more careful. I would start by resetting all vmstate versions
> to 1!

Why would you reset it? Keeping 3 (or whatever it will be by then) as
the first serious supported version shouldn't hurt and probably avoids
some confusion.

Kevin