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authorHugh Dickins <hugh@veritas.com>2005-10-29 18:16:36 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-29 21:40:42 -0700
commit69b0475456ff7ef520e16f69d7a15c0d68b74e64 (patch)
tree3e70d47f16437254eff3b3cca4aa275be1b5e275 /arch/arm/mm
parent60ec5585496871345c1a8113d7b60ed9d9474866 (diff)
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[PATCH] mm: arm ready for split ptlock
Prepare arm for the split page_table_lock: three issues. Signal handling's preserve and restore of iwmmxt context currently involves reading and writing that context to and from user space, while holding page_table_lock to secure the user page(s) against kswapd. If we split the lock, then the structure might span two pages, secured by to read into and write from a kernel stack buffer, copying that out and in without locking (the structure is 160 bytes in size, and here we're near the top of the kernel stack). Or would the overhead be noticeable? arm_syscall's cmpxchg emulation use pte_offset_map_lock, instead of pte_offset_map and mm-wide page_table_lock; and strictly, it should now also take mmap_sem before descending to pmd, to guard against another thread munmapping, and the page table pulled out beneath this thread. Updated two comments in fault-armv.c. adjust_pte is interesting, since its modification of a pte in one part of the mm depends on the lock held when calling update_mmu_cache for a pte in some other part of that mm. This can't be done with a split page_table_lock (and we've already taken the lowest lock in the hierarchy here): so we'll have to disable split on arm, unless CONFIG_CPU_CACHE_VIPT to ensures adjust_pte never used. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r--arch/arm/mm/fault-armv.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index be4ab3d..7fc1b35 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -26,6 +26,11 @@ static unsigned long shared_pte_mask = L_PTE_CACHEABLE;
/*
* We take the easy way out of this problem - we make the
* PTE uncacheable. However, we leave the write buffer on.
+ *
+ * Note that the pte lock held when calling update_mmu_cache must also
+ * guard the pte (somewhere else in the same mm) that we modify here.
+ * Therefore those configurations which might call adjust_pte (those
+ * without CONFIG_CPU_CACHE_VIPT) cannot support split page_table_lock.
*/
static int adjust_pte(struct vm_area_struct *vma, unsigned long address)
{
@@ -127,7 +132,7 @@ void __flush_dcache_page(struct address_space *mapping, struct page *page);
* 2. If we have multiple shared mappings of the same space in
* an object, we need to deal with the cache aliasing issues.
*
- * Note that the page_table_lock will be held.
+ * Note that the pte lock will be held.
*/
void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
{
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