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

On 03/03/16 19:19, Will Deacon wrote:

On Thu, Mar 03, 2016 at 02:03:08PM -0500, Christopher Covington wrote:

quoted

On 03/03/2016 01:27 PM, Robin Murphy wrote:

quoted

On 03/03/16 17:59, Christopher Covington wrote:

quoted

quoted

quoted

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.

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

[1] https://lkml.org/lkml/2015/10/13/641

Cheers
Suzuki