[PATCH 3.10 19/86] mm: use paravirt friendly ops for NUMA hinting ptes

Greg Kroah-Hartman
2014-05-29T04:38:16Z

From: Mel Gorman <mgorman@suse.de>

commit 29c7787075c92ca8af353acd5301481e6f37082f upstream.

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 <mgorman@suse.de>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Tested-by: David Vrabel <david.vrabel@citrix.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Noonan <steven@uplinklabs.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/asm-generic/pgtable.h | 31 +++++++++++++++++++++++--------
1 file changed, 23 insertions(+), 8 deletions(-)

--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -620,32 +620,47 @@ static inline int pmd_numa(pmd_t pmd)
#ifndef pte_mknonnuma
static inline pte_t pte_mknonnuma(pte_t pte)
{
- pte = pte_clear_flags(pte, _PAGE_NUMA);
- return pte_set_flags(pte, _PAGE_PRESENT|_PAGE_ACCESSED);
+ pteval_t val = pte_val(pte);
+
+ val &= ~_PAGE_NUMA;
+ val |= (_PAGE_PRESENT|_PAGE_ACCESSED);
+ return __pte(val);
}
#endif

#ifndef pmd_mknonnuma
static inline pmd_t pmd_mknonnuma(pmd_t pmd)
{
- pmd = pmd_clear_flags(pmd, _PAGE_NUMA);
- return pmd_set_flags(pmd, _PAGE_PRESENT|_PAGE_ACCESSED);
+ pmdval_t val = pmd_val(pmd);
+
+ val &= ~_PAGE_NUMA;
+ val |= (_PAGE_PRESENT|_PAGE_ACCESSED);
+
+ return __pmd(val);
}
#endif

#ifndef pte_mknuma
static inline pte_t pte_mknuma(pte_t pte)
{
- pte = pte_set_flags(pte, _PAGE_NUMA);
- return pte_clear_flags(pte, _PAGE_PRESENT);
+ pteval_t val = pte_val(pte);
+
+ val &= ~_PAGE_PRESENT;
+ val |= _PAGE_NUMA;
+
+ return __pte(val);
}
#endif

#ifndef pmd_mknuma
static inline pmd_t pmd_mknuma(pmd_t pmd)
{
- pmd = pmd_set_flags(pmd, _PAGE_NUMA);
- return pmd_clear_flags(pmd, _PAGE_PRESENT);
+ pmdval_t val = pmd_val(pmd);
+
+ val &= ~_PAGE_PRESENT;
+ val |= _PAGE_NUMA;
+
+ return __pmd(val);
}
#endif
#else