mm: use paravirt friendly ops for NUMA hinting ptes

David Vrabel identified a regression when using automatic NUMA balancing
under Xen whereby page table entries were getting corrupted due to the
use of native PTE operations.  Quoting him

	Xen PV guest page tables require that their entries use machine
	addresses if the preset bit (_PAGE_PRESENT) is set, and (for
	successful migration) non-present PTEs must use pseudo-physical
	addresses.  This is because on migration MFNs in present PTEs are
	translated to PFNs (canonicalised) so they may be translated back
	to the new MFN in the destination domain (uncanonicalised).

	pte_mknonnuma(), pmd_mknonnuma(), pte_mknuma() and pmd_mknuma()
	set and clear the _PAGE_PRESENT bit using pte_set_flags(),
	pte_clear_flags(), etc.

	In a Xen PV guest, these functions must translate MFNs to PFNs
	when clearing _PAGE_PRESENT and translate PFNs to MFNs when setting
	_PAGE_PRESENT.

His suggested fix converted p[te|md]_[set|clear]_flags to using
paravirt-friendly ops but this is overkill.  He suggested an alternative
of using p[te|md]_modify in the NUMA page table operations but this is
does more work than necessary and would require looking up a VMA for
protections.

This patch modifies the NUMA page table operations to use paravirt
friendly operations to set/clear the flags of interest.  Unfortunately
this will take a performance hit when updating the PTEs on
CONFIG_PARAVIRT but I do not see a way around it that does not break
Xen.

Signed-off-by: Mel Gorman <[email protected]>
Acked-by: David Vrabel <[email protected]>
Tested-by: David Vrabel <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Anvin <[email protected]>
Cc: Fengguang Wu <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Steven Noonan <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Cc: Cyrill Gorcunov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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