commit 86e5bcfd0a39960e68475a5a6108088176d98aae
Author: Wolfgang Mauerer <wolfgang.mauerer@domain.hid>
Date:   Sun Jan 24 23:13:30 2010 +0100

    x86: Fix root domain state restoring on exception return

diff --git a/arch/x86/kernel/ipipe.c b/arch/x86/kernel/ipipe.c
index 4442d96..b8a6ec7 100644
--- a/arch/x86/kernel/ipipe.c
+++ b/arch/x86/kernel/ipipe.c
@@ -702,19 +702,22 @@ static int __ipipe_xlate_signo[] = {
 
 int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector)
 {
-	unsigned long flags;
+	bool restore_flags = false;
+	unsigned long flags = 0;
+	unsigned long regflags;
+	unsigned long rawflags;
 
 	/* Pick up the root domain state of the interrupted context. */
 	local_save_flags(flags);
 
-	if (ipipe_root_domain_p) {
+	if (ipipe_root_domain_p && irqs_disabled_hw()) {
 		/*
 		 * Replicate hw interrupt state into the virtual mask before
 		 * calling the I-pipe event handler over the root domain. Also
 		 * required later when calling the Linux exception handler.
 		 */
-		if (irqs_disabled_hw())
-			local_irq_disable();
+		local_irq_save(flags);
+		restore_flags = true;
 	}
 #ifdef CONFIG_KGDB
 	/* catch exception KGDB is interested in over non-root domains */
@@ -725,16 +728,32 @@ int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector)
 #endif /* CONFIG_KGDB */
 
 	if (unlikely(ipipe_trap_notify(vector, regs))) {
-		local_irq_restore_nosync(flags);
+		if (restore_flags)
+			local_irq_restore_nosync(flags);
 		return 1;
 	}
 
-	/*
-	 * 32-bit: In case we migrated to root domain inside the event
-	 * handler, restore the original IF from exception entry as the
-	 * low-level return code will evaluate it.
-	 */
-	__fixup_if(raw_irqs_disabled_flags(flags), regs);
+	/* NOTE: We don't need a fixup when we entered via non-root domain,
+	 * and also not when we entered over a root domain with interrupts
+	 * enabled. */
+	if (restore_flags) {
+		regflags = regs->flags;
+		rawflags = __raw_local_save_flags();
+
+		printk("before fixup: rawflags: %lx, flags: %lx, "
+		       "regs->flags: %lx\n", rawflags, flags, regs->flags);
+
+		__fixup_if(raw_irqs_disabled_flags(flags), regs);
+
+		printk("after fixup: rawflags: %lx, flags: %lx, "
+		       "regs->flags: %lx\n", rawflags, flags, regs->flags);
+
+//		if (regs->flags != regflags) {
+//			dump_stack();
+//			ipipe_trace_panic_dump();
+//			panic("__fixup_if did something for real!\n");
+//		}  
+	}
 
 	if (unlikely(!ipipe_root_domain_p)) {
 		/* Detect unhandled faults over non-root domains. */
@@ -770,21 +789,26 @@ int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector)
 	 * Relevant for 64-bit: Restore root domain state as the low-level
 	 * return code will not align it to regs.flags.
 	 */
-	local_irq_restore_nosync(flags);
+	if (restore_flags)
+		local_irq_restore_nosync(flags);
 
 	return 0;
 }
 
 int __ipipe_divert_exception(struct pt_regs *regs, int vector)
 {
-	unsigned long flags;
-
-	/* Same root state handling as in __ipipe_handle_exception. */
-	local_save_flags(flags);
+	bool restore_flags = false;
+	unsigned long flags = 0;
 
 	if (ipipe_root_domain_p) {
-		if (irqs_disabled_hw())
-			local_irq_disable();
+		if (irqs_disabled_hw()) {
+			/*
+			 * Same root state handling as in
+			 * __ipipe_handle_exception.
+			 */
+			local_irq_save(flags);
+			restore_flags = true;
+		}
 	}
 #ifdef CONFIG_KGDB
 	/* catch int1 and int3 over non-root domains */
@@ -804,16 +828,20 @@ int __ipipe_divert_exception(struct pt_regs *regs, int vector)
 #endif /* CONFIG_KGDB */
 
 	if (unlikely(ipipe_trap_notify(vector, regs))) {
-		local_irq_restore_nosync(flags);
+		if (restore_flags)
+			local_irq_restore_nosync(flags);
 		return 1;
 	}
 
+	if (likely(ipipe_root_domain_p)) {
+		/* see __ipipe_handle_exception */
+		__fixup_if(raw_irqs_disabled(), regs);
+	}
+
 	/*
-	 * 32-bit: Due to possible migration inside the event handler, we have
-	 * to restore IF so that low-level return code sets the root domain
-	 * state correctly.
+	 * No need to restore root state in the 64-bit case, the Linux handler
+	 * and the return code will take care of it.
 	 */
-	__fixup_if(raw_irqs_disabled_flags(flags), regs);
 
 	return 0;
 }