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

[Alexander Graf <agraf@suse.de>]

On 21.05.2011, at 11:39, Andreas Färber wrote:

> Am 21.05.2011 um 03:58 schrieb Alexander Graf:
> 
>> Am 21.05.2011 um 00:37 schrieb Andreas Färber <andreas.faerber@web.de>:
>> 
>>> 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 :)
>>> 
>>> Nack, this does not fix ppc64 for me! How did you test it, Alex???
>> 
>> I booted a ppc64 kernel on a ppc64 Linux system with tcg and it booted fine for me. Maybe you're hitting yet another issue?
> 
> Which OpenBIOS did you use? The 32-bit version using mtsrin works now, but not the 64-bit HEAD version that I attached, which uses slb* instructions instead.

After some debugging, we tracked the 64-bit issue down to a bug in OpenBIOS, so things are fine in Qemu land now :)


Alex