On Fri, Nov 04, 2016 at 04:52:39PM +1100, Alexey Kardashevskiy wrote: > On 30/10/16 22:12, David Gibson wrote: > > When vmstate for the ppc cpu was introduced in a90db158 "target-ppc: > > Convert ppc cpu savevm to VMStateDescription", several "sanity check" > > fields were included, verifying that certain cpu parameters matched between > > source and destination. > > > > This turns out not to have been a good idea. For one thing it's redundant > > with existing checks for a compatible cpu version at either end. But more > > importantly the insns_flags and insns_flags2 checks actively break things: > > they expose what's essentially an internal TCG implementation detail in the > > migration stream. That means that when new instruction classes are added > > or rearranged, migration can break. > > > > This removes these ill-considered sanity checks. > > > > Signed-off-by: David Gibson <[email protected]> > > --- > > target-ppc/machine.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/target-ppc/machine.c b/target-ppc/machine.c > > index 62b9e94..453ef0a 100644 > > --- a/target-ppc/machine.c > > +++ b/target-ppc/machine.c > > @@ -602,10 +602,10 @@ const VMStateDescription vmstate_ppc_cpu = { > > /* FIXME: access_type? */ > > > > /* Sanity checking */ > > - VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU), > > - VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU), > > - VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU), > > - VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU), > > + VMSTATE_UNUSED(sizeof(target_ulong) /* msr_mask */ > > + + sizeof(uint64_t) /* insns_flags */ > > + + sizeof(uint64_t) /* insns_flags2 */ > > + + sizeof(uint32_t)), /* nb_BATs */ > > > This breaks migration to older QEMU: > > [email protected]:vmstate_load_field_error field "env.msr_mask" load > failed, ret = -22
Again, I don't think we generally support backwards migration.
That said, it would be nice here to do a "set to this field on
ourgoing migration, but ignore on incoming migration". Do you know a
way to do that?
a
>
>
>
> > VMSTATE_END_OF_LIST()
> > },
> > .subsections = (const VMStateDescription*[]) {
> >
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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