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-rw-r--r--include/linux/uaccess.h49
1 files changed, 46 insertions, 3 deletions
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index a48d7f11c7b..975c963e578 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -1,8 +1,43 @@
#ifndef __LINUX_UACCESS_H__
#define __LINUX_UACCESS_H__
+#include <linux/preempt.h>
#include <asm/uaccess.h>
+/*
+ * These routines enable/disable the pagefault handler in that
+ * it will not take any locks and go straight to the fixup table.
+ *
+ * They have great resemblance to the preempt_disable/enable calls
+ * and in fact they are identical; this is because currently there is
+ * no other way to make the pagefault handlers do this. So we do
+ * disable preemption but we don't necessarily care about that.
+ */
+static inline void pagefault_disable(void)
+{
+ inc_preempt_count();
+ /*
+ * make sure to have issued the store before a pagefault
+ * can hit.
+ */
+ barrier();
+}
+
+static inline void pagefault_enable(void)
+{
+ /*
+ * make sure to issue those last loads/stores before enabling
+ * the pagefault handler again.
+ */
+ barrier();
+ dec_preempt_count();
+ /*
+ * make sure we do..
+ */
+ barrier();
+ preempt_check_resched();
+}
+
#ifndef ARCH_HAS_NOCACHE_UACCESS
static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
@@ -30,14 +65,22 @@ static inline unsigned long __copy_from_user_nocache(void *to,
* do_page_fault() doesn't attempt to take mmap_sem. This makes
* probe_kernel_address() suitable for use within regions where the caller
* already holds mmap_sem, or other locks which nest inside mmap_sem.
+ * This must be a macro because __get_user() needs to know the types of the
+ * args.
+ *
+ * We don't include enough header files to be able to do the set_fs(). We
+ * require that the probe_kernel_address() caller will do that.
*/
#define probe_kernel_address(addr, retval) \
({ \
long ret; \
+ mm_segment_t old_fs = get_fs(); \
\
- inc_preempt_count(); \
- ret = __get_user(retval, addr); \
- dec_preempt_count(); \
+ set_fs(KERNEL_DS); \
+ pagefault_disable(); \
+ ret = __get_user(retval, (__force typeof(retval) __user *)(addr)); \
+ pagefault_enable(); \
+ set_fs(old_fs); \
ret; \
})