Re: [PATCH 1/9] x86, pkeys: add fault handling for PF_PK page fault bit

[Dave Hansen]

On 07/07/2016 07:40 AM, Mel Gorman wrote:
> On Thu, Jul 07, 2016 at 05:47:20AM -0700, Dave Hansen wrote:
>> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>> PF_PK means that a memory access violated the protection key
>> access restrictions.  It is unconditionally an access_error()
>> because the permissions set on the VMA don't matter (the PKRU
>> value overrides it), and we never "resolve" PK faults (like
>> how a COW can "resolve write fault).
>>
>> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> 
> An access fault gets propgated as SEGV_PKUERR. What happens if glibc
> does not recognise it?

It passes it through to the handler without any side-effects.  I don't
think it does anything differently with SEGV_* codes that it knows about
vs. unknown ones.  The only negative side-effect that I can think of is
that it won't have a nice error message for it.