Re: Cannot unwind through MIPS signal frames with ICACHE_REFILLS_WORKAROUND_WAR

[Ralf Baechle <ralf@linux-mips.org>]

On Tue, Nov 13, 2007 at 03:37:39PM +0100, Kevin D. Kissell wrote:

> True, though it should perhaps be noted that currently it's only on 4KSc/Sd
> systems (which I know you work on) where it's even possible for the stack
> *not* to have exec permissions, since the classical MIPS MMU gives
> execute permission to any page that is readable.

Disabling PROT_EXEC on a mapping tells the kernel it doesn't need to take
care of I-cache coherency.  So it's somewhat beneficial even in absence of
a protection bit in the actual TLB hardware.

Some of these performance optimizations are impossible because the kernel
can't have definate knowledge that certain addresses have never entered the
I-cache.

  Ralf