Re: [Qemu-devel] pseries-2.6 migration from QEMU-2.6 to QEMU-2.7 broken

[David Gibson]

On Thu, Sep 22, 2016 at 10:51:05AM +0530, Bharata B Rao wrote:
> Hi,
> 
> Nikunj and I realized that migrating pseries-2.6 guest from QEMU-2.6
> to newer QEMU-2.7 is broken like this:
> 
> qemu-system-ppc64: error while loading state for instance 0x0 of device 'cpu'
> qemu-system-ppc64: load of migration failed: Invalid argument
> 
> Bisecting tells us that 4e0806110c8b896ceff3490f15a616e8b3165efe
> (ppc: Add PPC_64H instruction flag to POWER7 and POWER8) is the
> first bad commit.  Along with this there are other 3 similar commits
> which add new bits to insns_flags and insns_flags2 fields of POWER7
> and POWER8 CPUs.
> 
> 4e0806110c8b896ceff3490f15a616e8b3165efe Adds PPC_64H to POWER7 and POWER8
> dfdd3e43620a6cd4f2be31da5a257c84a16fc000 Adds PPC_64BX to POWER7
> b781537560e3b968b6fe1395e3d07bd67f0009ba Adds PPC_CILDST to POWER7 and POWER8
> 7778a575c7055276afdd01737e9d1029a65f923d Adds PPC2_PM_ISA206 to POWER7 and 
> POWER8
> 
> 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.

Can you step me through how the new flags are breaking the migration?
It's not immediately obvious to me.

-- 
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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