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Subject[patch V4 part 4 20/24] x86/traps: Restructure #DB handling
Now that there are separate entry points, move the kernel/user_mode specifc
checks into the entry functions so the common handling code does not need
the extra mode checks. Make the code more readable while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/traps.c | 69 ++++++++++++++++++++++++------------------------
1 file changed, 35 insertions(+), 34 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -753,39 +753,12 @@ static __always_inline void debug_exit(u
*
* May run on IST stack.
*/
-static noinstr void handle_debug(struct pt_regs *regs, unsigned long dr6)
+static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
+ bool user_icebp)
{
struct task_struct *tsk = current;
- int user_icebp = 0;
int si_code;

- /*
- * 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 (unlikely(!user_mode(regs) && (dr6 & DR_STEP) &&
- is_sysenter_singlestep(regs))) {
- dr6 &= ~DR_STEP;
- if (!dr6)
- return;
- /*
- * else we might have gotten a single-step trap and hit a
- * watchpoint at the same time, in which case we should fall
- * through and handle the watchpoint.
- */
- }
-
- /*
- * 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.
- */
- if (!dr6 && user_mode(regs))
- user_icebp = 1;
-
/* Store the virtualized DR6 value */
tsk->thread.debugreg6 = dr6;

@@ -810,9 +783,7 @@ static noinstr void handle_debug(struct
if (v8086_mode(regs)) {
handle_vm86_trap((struct kernel_vm86_regs *) regs, 0,
X86_TRAP_DB);
- cond_local_irq_disable(regs);
- debug_stack_usage_dec();
- return;
+ goto out;
}

if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
@@ -826,9 +797,12 @@ static noinstr void handle_debug(struct
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
regs->flags &= ~X86_EFLAGS_TF;
}
+
si_code = get_si_code(tsk->thread.debugreg6);
if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
send_sigtrap(regs, 0, si_code);
+
+out:
cond_local_irq_disable(regs);
debug_stack_usage_dec();
}
@@ -837,7 +811,27 @@ static __always_inline void exc_debug_ke
unsigned long dr6)
{
nmi_enter();
- handle_debug(regs, dr6);
+ /*
+ * 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);
+
+ /*
+ * Catch SYSENTER with TF set and clear DR_STEP. If this hit a
+ * watchpoint at the same time then that will still be handled.
+ */
+ if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
+ dr6 &= ~DR_STEP;
+
+ /*
+ * If DR6 is zero, no point in trying to handle it. The kernel is
+ * not using INT1.
+ */
+ if (dr6)
+ handle_debug(regs, dr6, false);
+
nmi_exit();
}

@@ -845,7 +839,14 @@ static __always_inline void exc_debug_us
unsigned long dr6)
{
idtentry_enter(regs);
- handle_debug(regs, dr6);
+ 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.
+ */
+ handle_debug(regs, dr6, !dr6);
idtentry_exit(regs);
}

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