[PATCH] Handle spurious page fault for hugetlb region
The hugetlb pages are currently pre-faulted. At the time of mmap of
hugepages, we populate the new PTEs. It is possible that HW has already
cached some of the unused PTEs internally. These stale entries never
get a chance to be purged in existing control flow.
This patch extends the check in page fault code for hugepages. Check if
a faulted address falls with in size for the hugetlb file backing it.
We return VM_FAULT_MINOR for these cases (assuming that the arch
specific page-faulting code purges the stale entry for the archs that
need it).
Signed-off-by: Rohit Seth <rohit.seth@intel.com>
[ This is apparently arguably an ia64 port bug. But the code won't
hurt, and for now it fixes a real problem on some ia64 machines ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index e670b0d..42cb7d70 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -155,11 +155,24 @@
{
file->f_op = &hugetlbfs_file_operations;
}
+
+static inline int valid_hugetlb_file_off(struct vm_area_struct *vma,
+ unsigned long address)
+{
+ struct inode *inode = vma->vm_file->f_dentry->d_inode;
+ loff_t file_off = address - vma->vm_start;
+
+ file_off += (vma->vm_pgoff << PAGE_SHIFT);
+
+ return (file_off < inode->i_size);
+}
+
#else /* !CONFIG_HUGETLBFS */
#define is_file_hugepages(file) 0
#define set_file_hugepages(file) BUG()
#define hugetlb_zero_setup(size) ERR_PTR(-ENOSYS)
+#define valid_hugetlb_file_off(vma, address) 0
#endif /* !CONFIG_HUGETLBFS */
diff --git a/mm/memory.c b/mm/memory.c
index ae8161f..8c88b97 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2045,8 +2045,18 @@
inc_page_state(pgfault);
- if (is_vm_hugetlb_page(vma))
- return VM_FAULT_SIGBUS; /* mapping truncation does this. */
+ if (unlikely(is_vm_hugetlb_page(vma))) {
+ if (valid_hugetlb_file_off(vma, address))
+ /* We get here only if there was a stale(zero) TLB entry
+ * (because of HW prefetching).
+ * Low-level arch code (if needed) should have already
+ * purged the stale entry as part of this fault handling.
+ * Here we just return.
+ */
+ return VM_FAULT_MINOR;
+ else
+ return VM_FAULT_SIGBUS; /* mapping truncation does this. */
+ }
/*
* We need the page table lock to synchronize with kswapd