[PATCH] powerpc: book3s: kvm: Use the saved dsisr and dar values

[Alexander Graf]

> Am 20.12.2013 um 05:37 schrieb "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>:
> 
> Alexander Graf <agraf at suse.de> writes:
> 
>>> Am 19.12.2013 um 08:02 schrieb "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>:
>>> 
>>> Alexander Graf <agraf at suse.de> writes:
>>> 
>>>>> On 11.11.2013, at 15:02, Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com> wrote:
>>>>> 
>>>>> From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
>>>>> 
>>>>> Don't try to compute these values.
>>>>> 
>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
>>>>> ---
>>>>> 
>>>>> NOTE: I am not sure why we were originally computing dsisr and dar. So may be
>>>>> we need a variant of this patch. But with this and the additional patch
>>>>> "powerpc: book3s: PR: Enable Little Endian PR guest" I am able to get a Little Endian
>>>>> PR guest to boot.
>>>> 
>>>> It's quite easy to find out - git blame tells you all the history and points you to commit ca7f4203b.
>>>> 
>>>> commit ca7f4203b9b66e12d0d9968ff7dfe781f3a9695a
>>>> Author: Alexander Graf <agraf at suse.de>
>>>> Date:   Wed Mar 24 21:48:28 2010 +0100
>>>> 
>>>>   KVM: PPC: Implement alignment interrupt
>>>> 
>>>>   Mac OS X has some applications - namely the Finder - that require alignment
>>>>   interrupts to work properly. So we need to implement them.
>>>> 
>>>>   But the spec for 970 and 750 also looks different. While 750 requires the
>>>>   DSISR and DAR fields to reflect some instruction bits (DSISR) and the fault
>>>>   address (DAR), the 970 declares this as an optional feature. So we need
>>>>   to reconstruct DSISR and DAR manually.
>>>> 
>>>>   Signed-off-by: Alexander Graf <agraf at suse.de>
>>>>   Signed-off-by: Avi Kivity <avi at redhat.com>
>>>> 
>>>> Read this as "on 970, alignment interrupts don't give us DSISR and DAR of the faulting instruction" as otherwise I wouldn't have implemented it.
>>>> 
>>>> So this is clearly a nack on this patch :).
>>> 
>>> I can possibly do a if (cpu_has_feature(CPU_FTR_ARCH_201)). But do we need
>>> to do that ? According to Paul we should always find DAR.
>> 
>> Paul only mentioned DAR, not DSISR. Please verify whether 970 gives us a proper DAR value - we can then remove that part.
>> 
>> But for DSISR I'm not convinced CPUs above 970 handle this
>> correctly. So we would at least need a guest cpu check to find out
>> whether the vcpu expects a working dsisr and emulate it then.
> 
>> 
>> I don't really fully understand the problem though. Why does the
>> calculation break at all for you?
> 
> 
> IIRC this was to get little endian PR setup to work. This is to avoid
> handling new instructions, because in little endian mode we get
> alignment interrupt for a larger instructon set

Ok, please limit dar/dsisr calculation to book3s_32 vcpus then :).

Alex

> 
> -aneesh
>