On Thu, Sep 22, 2016 at 02:34:19PM +0530, Nikunj A Dadhania wrote:
> Benjamin Herrenschmidt <b...@kernel.crashing.org> writes:
>
> > On Thu, 2016-09-22 at 11:45 +0530, Bharata B Rao wrote:
> >> On Thu, Sep 22, 2016 at 04:07:21PM +1000, Benjamin Herrenschmidt wrote:
> >> >
> >> > On Thu, 2016-09-22 at 10:51 +0530, Bharata B Rao wrote:
> >> > >
> >> > > The flag values are expected to remain same for a machine version for
> >> > > the migration to succeed, but this expectation is broken now. Should
> >> > > we make the addition of these flags conditional on machine type
> >> > > version ?
> >> > > But these flags are part of POWER8 CPU definition which is common for
> >> > > both pseries and upcoming powernv.
> >> >
> >> > Does this affect KVM ? (And if yes why on earth would KVM give a flying
> >> > f*** about the TCG instruction flags ?) ... If not, then I think we can
> >> > safely not care.
> >>
> >> Yes, KVM migration is broken.
> >
> > Argh then ... stupid design in QEMU. We can't fix anything without
> > breaking migration, yay !
>
> Looking back in the history of the code:
>
> commit: a90db1584a00dc1d1439dc7729d99674b666b85e (target-ppc: Convert
> ppc cpu savevm to VMStateDescription) added this:
>
> + /* Sanity checking */
> + VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> + VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
>
> These flags weren't part of vmstate, I am not sure what was the reason
> behind adding it though. Its a bit old, Alexey do you remember?
>
> > I don't know what to do to fix that to be honest. Do we have a way to filter
> > what flags actually matter and filter things out when KVM is enabled ?
>
> Something like this works for KVM:
>
> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> index 4820f22..1cf3779 100644
> --- a/target-ppc/machine.c
> +++ b/target-ppc/machine.c
> @@ -563,8 +563,8 @@ const VMStateDescription vmstate_ppc_cpu = {
>
> /* Sanity checking */
> VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
> - VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> - VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
> + VMSTATE_UNUSED(sizeof(target_ulong)), /* was _EQUAL(env.insns_flags)
> */
> + VMSTATE_UNUSED(sizeof(target_ulong)), /* was
> _EQUAL(env.insns_flags2) */
> VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU),
> VMSTATE_END_OF_LIST()
> },
This looks like the right solution to me. AFAICT this was just a
sanity check that wasn't thought through well enough.
> TCG migration still remains broken with this.
Uh.. why?
--
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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