On 09/20/2016 04:24 PM, Thomas Huth wrote:
> On 20.09.2016 16:04, Cédric Le Goater wrote:
>> On 09/20/2016 02:24 PM, Cédric Le Goater wrote:
>>> On 09/20/2016 01:44 PM, Thomas Huth wrote:
>>>>  Hi,
>>>> when I try to run my guest in KVM-PR mode, current QEMU refuses to start:
>>>>   $ sudo qemu-system-ppc64 -M pseries,accel=kvm,kvm-type=PR \
>>>>                            -nographic -vga none -cpu POWER8
>>>>   qemu: fatal: Unknown MMU model 851972
>>>> ... followed by a useless register dump. I've bisected the issue, and it
>>>> seems like the problem has been introduced by this commit here:
>>>>   commit 4322e8ced5aaac7191958f09622d199fe61e2d87
>>>>   ppc: Fix 64K pages support in full emulation
>>>> Seems like KVM PR is using the "degraded" ISA variants (without the 1TB
>>>> segments), but the new POWERPC_MMU_64K flag has not been added to those.
>>>> Has this been done on purpose, or was this just by accident?
>>> The "degraded" architecture support has some history behind it :
>>>  commit 126a79300971 added it
>>>  commit aa4bb5875231 removed it.
>>>  commit ba3ecda05e93 readded it.
>>>  commit 4322e8ced5aa forgot about it again
>>>> I can make KVM PR working again with the following patch:
>>> I think this is correct. Let's wait for Ben to chime in :)
>> So I confirm the bug and the fix. 
>> There are other issues after in the guest (kernel crashing). But I think
>> these are related to TM which is not supported in KVM-PR. I am not sure
>> where we are on that point.
> There was a patch some months ago:
> https://lists.gnu.org/archive/html/qemu-ppc/2016-04/msg00046.html
> ... but I think it has never been included, as far as I can see.

and with that patch, the guest fully boots. But David had some concerns
on the way it is done. It would be nice to put some cycle on this. 



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