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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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From: Michael Ellerman <patch-notifications@ellerman.id.au>
Cc: Michael Neuling <michael.neuling@au1.ibm.com>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: powerpc/mm: Fix spurrious segfaults on radix with Autonuma
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Date: Fri, 10 Feb 2017 00:20:09 +1100 (AEDT)
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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@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@linux.vnet.ibm.com>
> Acked-by: Balbir Singh <bsingharora@gmail.com>

Applied to powerpc fixes, thanks.

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

cheers