kernel virtual memory access (from app) does not generate segfault

[Jamie Lokier]

Russell King - ARM Linux wrote:
> On Tue, Apr 20, 2010 at 11:31:06PM +0100, Jamie Lokier wrote:
> > But a possible NAK: What happens when the kernel does get/put_user()
> > on an address > TASK_SIZE with kernel-only mapping?  user_mode()
> > returns 0, so the LDRT will loop in the kernel, won't it?
> 
> No - the first data fault will cause the pgd entry to be copied, and then
> the subsequent data fault will be a permission fault.
> 
> The difference between instruction faults and data faults is that we
> always interpret instruction faults on pre-ARMv6 CPUs as a 'translation
> fault' rather than a permission fault since they can't tell us what the
> problem was.

Subtle, but nice.

So are the ifar_info and ifsr_info tables completely redundant
pre-ARMv6, or is it just ifsr_info?

-- Jamie