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From: Thomas Huth <thuth@redhat.com>
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Date: Tue, 20 Sep 2016 16:24:00 +0200
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Subject: Re: [Qemu-devel] [Qemu-ppc] KVM-PR is broken with current QEMU
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To: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= <clg@kaod.org>, qemu-ppc@nongnu.org
Cc: QEMU Developers <qemu-devel@nongnu.org>, David Gibson <david@gibson.dropbear.id.au>

On 20.09.2016 16:04, C=C3=A9dric Le Goater wrote:
> On 09/20/2016 02:24 PM, C=C3=A9dric 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 st=
art:
>>>
>>>   $ sudo qemu-system-ppc64 -M pseries,accel=3Dkvm,kvm-type=3DPR \
>>>                            -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 1=
TB
>>> segments), but the new POWERPC_MMU_64K flag has not been added to tho=
se.
>>> 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 :)
>=20
> So I confirm the bug and the fix.=20
>=20
> There are other issues after in the guest (kernel crashing). But I thin=
k
> 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.

 Thomas