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

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Alexander Graf <agraf@suse.de> writes:

> On 11.11.2013, at 15:02, Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> wrote:
>
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> 
>> Don't try to compute these values.
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@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@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@suse.de>
>     Signed-off-by: Avi Kivity <avi@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.

-aneesh