Re: [Qemu-devel] [RFC 17/17] pseries: Default to POWER8 compatibility mode

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 1913 bytes --]

On Sun, Oct 30, 2016 at 10:12:08PM +1100, David Gibson wrote:
> Currently, the pseries machine defaults to running in the "raw" mode of
> whatever the CPU version is - that is, without any compatibility options
> enabled in the CPU.
> 
> However, migration is only really safe in "raw" mode if source and
> destination have exactly the same cpu model.  Since HV KVM exposes the
> version of the host CPU to the guest, that means "raw" migration between
> hosts with different minor revisions isn't strictly safe, although it
> generally works in practice.
> 
> To allow this sort of migration in a more clearly defined way, instead
> default to running in POWER8 compatibility mode - if an older CPU is used
> that will automatically be downgraded to the higest available compatibility
> mode.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Ugh, sorry.  When I said minimally tested I did mean that it passed
make check, but unfortunately I was sloppy and this last patch breaks
a bunch of stuff.

> ---
>  hw/ppc/spapr.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 2aa0900..8c18dc8 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2194,6 +2194,7 @@ static void spapr_machine_initfn(Object *obj)
>                                      " (required for memory hot-unplug support)",
>                                      NULL);
>  
> +    spapr->max_compat_pvr = CPU_POWERPC_LOGICAL_2_07; /* POWER8 */
>      object_property_add(obj, "max-cpu-compat", "str",
>                          ppc_compat_prop_get, ppc_compat_prop_set,
>                          NULL, &spapr->max_compat_pvr, &error_fatal);

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]