[PATCH] powerpc/mm: Fix spurrious segfaults on radix with Autonuma

[Balbir Singh]

On Fri, Feb 03, 2017 at 05:10:28PM +1100, Benjamin Herrenschmidt wrote:
> When autonuma marks a PTE inaccessible it clears all the protection
> bits but leave the PTE valid.
> 
> With the Radix MMU, an attempt at executing from such a PTE will
> take a fault with bit 35 of SRR1 set "SRR1_ISI_N_OR_G".
> 
> It is thus incorrect to treat all such faults as errors. We should
> pass them to handle_mm_fault() for autonuma to deal with. The case
> of pages that are really not executable is handled by the existing
> test for VM_EXEC further down.
> 
> That leaves us with catching the kernel attempts at executing user
> pages. We can catch that earlier, even before we do find_vma.
> 
> It is never valid on powerpc for the kernel to take an exec fault
> to begin with. So fold that test with the existing test for the
> kernel faulting on kernel addresses to bail out early.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Fixes: 1d18ad0 ("powerpc/mm: Detect instruction fetch denied and report")
> Fixes: 0ab5171 ("powerpc/mm: Fix no execute fault handling on pre-POWER5")
> ---
>

Acked-by: Balbir Singh <bsingharora at gmail.com>