From 77b98fad7441345d09be55cde53e379c4396bf81 Mon Sep 17 00:00:00 2001
From: "K.Prasad" <prasad@linux.vnet.ibm.com>
Date: Mon, 1 Jun 2009 23:44:08 +0530
Subject: [PATCH] --- yaml --- r: 169663 b: refs/heads/master c:
 08d68323d1f0c34452e614263b212ca556dae47f h: refs/heads/master i:   169661:
 27d39f26f7f474c67759d76213cd2d09c73e534d   169659:
 1fbd7070f13c38cf1dc63fd066feb47c749d6f70   169655:
 2d5a9af5ef6c096c53632f527a9062c8e2255128   169647:
 4d74a38072c72821343c8dc3ffae378fb03175e8   169631:
 b5d4487a21e3c92144561a734a84453f3ba1cb68   169599:
 2e6fb7e882f6a77e69a031f20f74a6e9aa8d75b1 v: v3

---
 [refs]                        |  2 +-
 trunk/arch/x86/kernel/traps.c | 69 ++++++++++++-----------------------
 2 files changed, 25 insertions(+), 46 deletions(-)

diff --git a/[refs] b/[refs]
index 43fbfc1bf9e2..01833232a908 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0067f1297241ea567f2b22a455519752d70fcca9
+refs/heads/master: 08d68323d1f0c34452e614263b212ca556dae47f
diff --git a/trunk/arch/x86/kernel/traps.c b/trunk/arch/x86/kernel/traps.c
index a1d288327ff0..de9913247dd0 100644
--- a/trunk/arch/x86/kernel/traps.c
+++ b/trunk/arch/x86/kernel/traps.c
@@ -529,73 +529,52 @@ asmlinkage __kprobes struct pt_regs *sync_regs(struct pt_regs *eregs)
 dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
 	struct task_struct *tsk = current;
-	unsigned long condition;
+	unsigned long dr6;
 	int si_code;
 
-	get_debugreg(condition, 6);
+	get_debugreg(dr6, 6);
 
+	/* 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_DEBUGCTLMSR);
 	tsk->thread.debugctlmsr = 0;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
+	/* Store the virtualized DR6 value */
+	tsk->thread.debugreg6 = dr6;
+
+	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
 						SIGTRAP) == NOTIFY_STOP)
 		return;
 
 	/* It's safe to allow irq's after DR6 has been saved */
 	preempt_conditional_sti(regs);
 
-	/* Mask out spurious debug traps due to lazy DR7 setting */
-	if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
-		if (!tsk->thread.debugreg7)
-			goto clear_dr7;
+	if (regs->flags & X86_VM_MASK) {
+		handle_vm86_trap((struct kernel_vm86_regs *) regs,
+				error_code, 1);
+		return;
 	}
 
-#ifdef CONFIG_X86_32
-	if (regs->flags & X86_VM_MASK)
-		goto debug_vm86;
-#endif
-
-	/* Save debug status register where ptrace can see it */
-	tsk->thread.debugreg6 = condition;
-
 	/*
-	 * Single-stepping through TF: make sure we ignore any events in
-	 * kernel space (but re-enable TF when returning to user mode).
+	 * Single-stepping through system calls: ignore any exceptions in
+	 * kernel space, but re-enable TF when returning to user mode.
+	 *
+	 * We already checked v86 mode above, so we can check for kernel mode
+	 * by just checking the CPL of CS.
 	 */
-	if (condition & DR_STEP) {
-		if (!user_mode(regs))
-			goto clear_TF_reenable;
+	if ((dr6 & DR_STEP) && !user_mode(regs)) {
+		tsk->thread.debugreg6 &= ~DR_STEP;
+		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+		regs->flags &= ~X86_EFLAGS_TF;
 	}
-
-	si_code = get_si_code(condition);
-	/* Ok, finally something we can handle */
-	send_sigtrap(tsk, regs, error_code, si_code);
-
-	/*
-	 * Disable additional traps. They'll be re-enabled when
-	 * the signal is delivered.
-	 */
-clear_dr7:
-	set_debugreg(0, 7);
+	si_code = get_si_code(tsk->thread.debugreg6);
+	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
+		send_sigtrap(tsk, regs, error_code, si_code);
 	preempt_conditional_cli(regs);
-	return;
 
-#ifdef CONFIG_X86_32
-debug_vm86:
-	/* reenable preemption: handle_vm86_trap() might sleep */
-	dec_preempt_count();
-	handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
-	conditional_cli(regs);
-	return;
-#endif
-
-clear_TF_reenable:
-	set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-	regs->flags &= ~X86_EFLAGS_TF;
-	preempt_conditional_cli(regs);
 	return;
 }