1 files changed, 125 insertions, 0 deletions

diff --git a/recipes-kernel/linux/linux-ti33x-psp-3.2/3.2.22/0008-thp-avoid-atomic64_read-in-pmd_read_atomic-for-32bit.patch b/recipes-kernel/linux/linux-ti33x-psp-3.2/3.2.22/0008-thp-avoid-atomic64_read-in-pmd_read_atomic-for-32bit.patch
new file mode 100644
index 00000000..79be9e0f
--- /dev/null
+++ b/recipes-kernel/linux/linux-ti33x-psp-3.2/3.2.22/0008-thp-avoid-atomic64_read-in-pmd_read_atomic-for-32bit.patch
@@ -0,0 +1,125 @@
+From dcfb4634621189a74522dee4d0dab8b5c1786b02 Mon Sep 17 00:00:00 2001
+From: Andrea Arcangeli <aarcange@redhat.com>
+Date: Wed, 20 Jun 2012 12:52:57 -0700
+Subject: [PATCH 08/46] thp: avoid atomic64_read in pmd_read_atomic for 32bit
+ PAE
+
+commit e4eed03fd06578571c01d4f1478c874bb432c815 upstream.
+
+In the x86 32bit PAE CONFIG_TRANSPARENT_HUGEPAGE=y case while holding the
+mmap_sem for reading, cmpxchg8b cannot be used to read pmd contents under
+Xen.
+
+So instead of dealing only with "consistent" pmdvals in
+pmd_none_or_trans_huge_or_clear_bad() (which would be conceptually
+simpler) we let pmd_none_or_trans_huge_or_clear_bad() deal with pmdvals
+where the low 32bit and high 32bit could be inconsistent (to avoid having
+to use cmpxchg8b).
+
+The only guarantee we get from pmd_read_atomic is that if the low part of
+the pmd was found null, the high part will be null too (so the pmd will be
+considered unstable).  And if the low part of the pmd is found "stable"
+later, then it means the whole pmd was read atomically (because after a
+pmd is stable, neither MADV_DONTNEED nor page faults can alter it anymore,
+and we read the high part after the low part).
+
+In the 32bit PAE x86 case, it is enough to read the low part of the pmdval
+atomically to declare the pmd as "stable" and that's true for THP and no
+THP, furthermore in the THP case we also have a barrier() that will
+prevent any inconsistent pmdvals to be cached by a later re-read of the
+*pmd.
+
+Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
+Cc: Jonathan Nieder <jrnieder@gmail.com>
+Cc: Ulrich Obergfell <uobergfe@redhat.com>
+Cc: Mel Gorman <mgorman@suse.de>
+Cc: Hugh Dickins <hughd@google.com>
+Cc: Larry Woodman <lwoodman@redhat.com>
+Cc: Petr Matousek <pmatouse@redhat.com>
+Cc: Rik van Riel <riel@redhat.com>
+Cc: Jan Beulich <jbeulich@suse.com>
+Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
+Tested-by: Andrew Jones <drjones@redhat.com>
+Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
+---
+ arch/x86/include/asm/pgtable-3level.h |   30 +++++++++++++++++-------------
+ include/asm-generic/pgtable.h         |   10 ++++++++++
+ 2 files changed, 27 insertions(+), 13 deletions(-)
+
+diff --git a/arch/x86/include/asm/pgtable-3level.h b/arch/x86/include/asm/pgtable-3level.h
+index 43876f1..cb00ccc 100644
+--- a/arch/x86/include/asm/pgtable-3level.h
++++ b/arch/x86/include/asm/pgtable-3level.h
+@@ -47,16 +47,26 @@ static inline void native_set_pte(pte_t *ptep, pte_t pte)
+  * they can run pmd_offset_map_lock or pmd_trans_huge or other pmd
+  * operations.
+  *
+- * Without THP if the mmap_sem is hold for reading, the
+- * pmd can only transition from null to not null while pmd_read_atomic runs.
+- * So there's no need of literally reading it atomically.
++ * Without THP if the mmap_sem is hold for reading, the pmd can only
++ * transition from null to not null while pmd_read_atomic runs. So
++ * we can always return atomic pmd values with this function.
+  *
+  * With THP if the mmap_sem is hold for reading, the pmd can become
+- * THP or null or point to a pte (and in turn become "stable") at any
+- * time under pmd_read_atomic, so it's mandatory to read it atomically
+- * with cmpxchg8b.
++ * trans_huge or none or point to a pte (and in turn become "stable")
++ * at any time under pmd_read_atomic. We could read it really
++ * atomically here with a atomic64_read for the THP enabled case (and
++ * it would be a whole lot simpler), but to avoid using cmpxchg8b we
++ * only return an atomic pmdval if the low part of the pmdval is later
++ * found stable (i.e. pointing to a pte). And we're returning a none
++ * pmdval if the low part of the pmd is none. In some cases the high
++ * and low part of the pmdval returned may not be consistent if THP is
++ * enabled (the low part may point to previously mapped hugepage,
++ * while the high part may point to a more recently mapped hugepage),
++ * but pmd_none_or_trans_huge_or_clear_bad() only needs the low part
++ * of the pmd to be read atomically to decide if the pmd is unstable
++ * or not, with the only exception of when the low part of the pmd is
++ * zero in which case we return a none pmd.
+  */
+-#ifndef CONFIG_TRANSPARENT_HUGEPAGE
+ static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
+ {
+        pmdval_t ret;
+@@ -74,12 +84,6 @@ static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
+ 
+        return (pmd_t) { ret };
+ }
+-#else /* CONFIG_TRANSPARENT_HUGEPAGE */
+-static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
+-{
+-       return (pmd_t) { atomic64_read((atomic64_t *)pmdp) };
+-}
+-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+ 
+ static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
+ {
+diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
+index 831924a..bc00876 100644
+--- a/include/asm-generic/pgtable.h
++++ b/include/asm-generic/pgtable.h
+@@ -484,6 +484,16 @@ static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
+        /*
+         * The barrier will stabilize the pmdval in a register or on
+         * the stack so that it will stop changing under the code.
++        *
++        * When CONFIG_TRANSPARENT_HUGEPAGE=y on x86 32bit PAE,
++        * pmd_read_atomic is allowed to return a not atomic pmdval
++        * (for example pointing to an hugepage that has never been
++        * mapped in the pmd). The below checks will only care about
++        * the low part of the pmd with 32bit PAE x86 anyway, with the
++        * exception of pmd_none(). So the important thing is that if
++        * the low part of the pmd is found null, the high part will
++        * be also null or the pmd_none() check below would be
++        * confused.
+         */
+ #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+        barrier();
+-- 
+1.7.10
+