The SDM says that debug exceptions clear BTF, and we need to keep
TIF_BLOCKSTEP in sync with BTF. Clear it unconditionally and improve
the comment.
I suspect that the fact that kmemcheck could cause TIF_BLOCKSTEP not
to be cleared was just an oversight.
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
arch/x86/kernel/traps.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index dd2c2e66c2e1..19e6cfa501e3 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -598,6 +598,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long
error_code)
dr6 &= ~DR6_RESERVED;
/*
+ * The SDM says "The processor clears the BTF flag when it
+ * generates a debug exception." Clear TIF_BLOCKSTEP to keep
+ * TIF_BLOCKSTEP in sync with the hardware BTF flag.
+ */
+ clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
+
+ /*
* If dr6 has no reason to give us about the origin of this trap,
* then it's very likely the result of an icebp/int01 trap.
* User wants a sigtrap for that.
@@ -612,11 +619,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long
error_code)
/* DR6 may or may not be cleared by the CPU */
set_debugreg(0, 6);
- /*
- * The processor cleared BTF, so don't mark that we need it set.
- */
- clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
-
/* Store the virtualized DR6 value */
tsk->thread.debugreg6 = dr6;
--
2.5.0
