Re: [PATCH V2 1/2] mm/autonuma: Let architecture override how the write bit should be stashed in a protnone pte.

From: Aneesh Kumar K.V
Date: Tue Feb 14 2017 - 00:56:08 EST

On Tuesday 14 February 2017 11:19 AM, Michael Ellerman wrote:
"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:

Autonuma preserves the write permission across numa fault to avoid taking
a writefault after a numa fault (Commit: b191f9b106ea " mm: numa: preserve PTE
write permissions across a NUMA hinting fault"). Architecture can implement
protnone in different ways and some may choose to implement that by clearing Read/
Write/Exec bit of pte. Setting the write bit on such pte can result in wrong
behaviour. Fix this up by allowing arch to override how to save the write bit
on a protnone pte.
This is pretty obviously a nop on arches that don't implement the new
hooks, but it'd still be good to get an ack from someone in mm land
before I merge it.

To get it apply cleanly you may need

They are strictly not needed after the saved write patch. But I didn't request to drop them, because the patch helps us
to get closer to the goal of no ste_pte_at() call on present ptes.