[PATCH v2 2/5] arm64: add ARMv8.2 id_aa64mmfr2 boiler plate

[James Morse]

Hi Suzuki,

On 04/03/16 10:20, Suzuki K. Poulose wrote:
> On 03/03/16 19:19, Will Deacon wrote:
>> On Thu, Mar 03, 2016 at 02:03:08PM -0500, Christopher Covington wrote:
>>> On 03/03/2016 01:27 PM, Robin Murphy wrote:
>>>> On 03/03/16 17:59, Christopher Covington wrote:
>>>>> swapper[0]: undefined instruction: pc=ffffff800808d730
>>>>> Code: d5380702 d5380721 f9017c02 f9018001 (d5380742)
>>>>> Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
>>>>> Modules linked in:
>>>>> CPU: 0 PID: 0 Comm: swapper Not tainted 4.5.0-rc6-next-20160303 #1
>>>>> Hardware name: (null) (DT)
>>>>> task: ffffff8008b2d980 ti: ffffff8008b20000 task.ti: ffffff8008b20000
>>>>> PC is at __cpuinfo_store_cpu+0x68/0x198
>>>>> LR is at cpuinfo_store_boot_cpu+0x28/0x50
>>>>>
>>>>> ffffff800808d730:       d5380742        mrs     x2, s3_0_c0_c7_2
>>>>
>>>> Hmm, per table C5-6 in the ARMv8 ARM (issue i), that's specifically a
>>>> reserved encoding, rather than an unallocated one, so it should read as
>>>> zero, not undef. What are you running on?
>>>
>>> QDF2432. I'll investigate.
>>
>> FWIW, I think the same issue was reported on qemu, so we may want to
>> handle this in the kernel anyway. We could either use alternatives on
>> the register read or handle the undef.

Alternatives would let us handle the QDF2432 case, but detecting the version of
qemu doesn't sound right. I will put together a series to handle the undef.


> We could use parts of the mrs emulation patch [1] to emulate only the above
> for kernel mode.

Thanks, I will see what I can poach!


James