From 2e917175e1ef147a527a9158b9f09773ec94c0bd Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Fri, 28 Nov 2014 11:53:59 +0100
Subject: [PATCH] xen: Speed up set_phys_to_machine() by using read-only
 mappings

Instead of checking at each call of set_phys_to_machine() whether a
new p2m page has to be allocated due to writing an entry in a large
invalid or identity area, just map those areas read only and react
to a page fault on write by allocating the new page.

This change will make the common path with no allocation much
faster as it only requires a single write of the new mfn instead
of walking the address translation tables and checking for the
special cases.

Suggested-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
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