1 files changed, 7 insertions, 0 deletions

diff --git a/include/asm-i386/ptrace.h b/include/asm-i386/ptrace.h
index 05532875e39e..7e0f2945d17d 100644
--- a/include/asm-i386/ptrace.h
+++ b/include/asm-i386/ptrace.h
@@ -61,6 +61,13 @@ struct pt_regs {
 struct task_struct;
 extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);
 
+/*
+ * user_mode_vm(regs) determines whether a register set came from user mode.
+ * This is true if V8086 mode was enabled OR if the register set was from
+ * protected mode with RPL-3 CS value.  This tricky test checks that with
+ * one comparison.  Many places in the kernel can bypass this full check
+ * if they have already ruled out V8086 mode, so user_mode(regs) can be used.
+ */
 static inline int user_mode(struct pt_regs *regs)
 {
         return (regs->xcs & 3) != 0;