powerpc/mm: Fix spurrious segfaults on radix with Autonuma

[Michael Ellerman]

On Fri, 2017-02-03 at 06:10:28 UTC, 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")
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> Acked-by: Balbir Singh <bsingharora at gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/d7df2443cd5f67fc6ee7c05a88e499

cheers