On Wed, Mar 30, 2016 at 12:32:42AM +0200, Arnd Bergmann wrote: > On Wednesday 30 March 2016 01:22:17 Yury Norov wrote: > > > > > > Undefined instruction in cpuinfo_store_boot_cpu() could be related > > > to the SYS_ID_AA64MMFR2_EL1 access that was recently added. > > > > > > What does the architecture say about reading unknown cpuid registers? > > > > > > Arnd > > > > ThunderX has some unimplemented system registers. AFAIR, attempt to access > > it > > causes data abort. > > Ok, if that is the case, maybe the read_cpuid() macro can be changed > so it contains a fixup for the trap? That should handle both data abort > and undefinstr. > > Arnd
Sounds alluring, but not clear what we'd return that way. I mean, how we'd distinguish between correct value and error code (0, -1 or whatever). But I think, we can do like this: val = read_cpuid_safe(reg, impossible_val); if (val == impossible_val) goto err; I think it will work for many cases. Yury.