Re: [Qemu-devel] [PATCH] Fix a bug in mtsr/mtsrin emulation on ppc64

[Alexander Graf]

On 21.05.2011, at 13:13, David Gibson wrote:

> On Sat, May 21, 2011 at 11:46:12AM +0200, Alexander Graf wrote:
>> 
>> On 21.05.2011, at 11:40, Andreas Färber wrote:
>> 
>>> Am 20.05.2011 um 09:40 schrieb Alexander Graf:
>>> 
>>>> On 20.05.2011, at 05:34, David Gibson wrote:
>>>> 
>>>>> Early ppc64 CPUs include a hack to partially simulate the ppc32 segment
>>>>> registers, by translating writes to them into writes to the SLB.  This is
>>>>> not used by any current Linux kernel, but it is used by the openbios used
>>>>> in the qemu mac99 model.
>>>>> 
>>>>> Commit 81762d6dd0d430d87024f2c83e9c4dcc4329fb7d, cleaning up the SLB
>>>>> handling introduced a bug in this code, breaking the openbios currently in
>>>>> qemu.  Specifically, there was an off by one error bitshuffling the
>>>>> register format used by mtsr into the format needed for the SLB load,
>>>>> causing the flag bits to end up in the wrong place.  This caused the
>>>>> storage keys to be wrong under openbios, meaning that the translation code
>>>>> incorrectly thought a legitimate access was a permission violation.
>>>>> 
>>>>> This patch fixes the bug, at the same time it fixes some build bug in the
>>>>> MMU debugging code (only exposed when DEBUG_MMU is enabled).
>>>> 
>>>> Thanks, applied to ppc-next :)
>>> 
>>> Hm. Don't you think we should split off the unrelated debug code fix for 
>>> bisecting?
>> 
>> Not sure if it's worth the effort. If you were bisecting before
>> that, you probably had DEBUG_MMU disabled anyways, because you'd
>> otherwise get build breakages before that specific commit anyways,
>> so the commit behaves as if it's only the SLB fix.
> 
> Right, I don't see how the debug fixes break bisect in any way.  Or
> least not in any way they werem't already broken.

Yup, let's just make sure to have you submit separate patches next time, so 
everyone is happy :)


Alex