From: Doug Chapman <dchapman@redhat.com>
Subject: [RHEL5.1 patch][xen] fix for hang when running gdb under xen
Date: Wed, 08 Aug 2007 13:56:41 -0400
Bugzilla: 246482
Message-Id: <1186595801.24308.10.camel@deimos.americas.hpqcorp.net>
Changelog: [XEN] ia64: fix for hang when running gdb


Fix for BZ 246482: dom0 hang when running gdb testsuite

This patch is already upstream in xen-unstable
http://lists.xensource.com/archives/html/xen-changelog/2007-07/msg00186.html

It touches only ia64 xen code and I have tested this by running the gdb
test suite.  The gdb suite now shows no regressions over the bare metal
RHEL5.1 kernel.  Without this patch any user can hang the entire system
by using watchpoints in gdb.

Note, formatting of the is consistent with the rest of xen code.

- Doug


--- xen/include/asm-ia64/linux-xen/asm/ptrace.h.gdbhang	2007-08-08 11:18:43.000000000 -0400
+++ xen/include/asm-ia64/linux-xen/asm/ptrace.h	2007-08-08 11:16:35.000000000 -0400
@@ -265,6 +265,9 @@
   /* given a pointer to a task_struct, return the user's pt_regs */
 # define ia64_task_regs(t)		(((struct pt_regs *) ((char *) (t) + IA64_STK_OFFSET)) - 1)
 # define ia64_psr(regs)			((struct ia64_psr *) &(regs)->cr_ipsr)
+#ifdef XEN
+# define guest_kernel_mode(regs)	(ia64_psr(regs)->cpl == 2)
+#endif
 # define user_mode(regs)		(((struct ia64_psr *) &(regs)->cr_ipsr)->cpl != 0)
 # define user_stack(task,regs)	((long) regs - (long) task == IA64_STK_OFFSET - sizeof(*regs))
 # define fsys_mode(task,regs)					\
--- xen/include/asm-ia64/debugger.h.gdbhang	2007-05-03 03:40:19.000000000 -0400
+++ xen/include/asm-ia64/debugger.h	2007-08-08 11:17:34.000000000 -0400
@@ -56,13 +56,6 @@
 #ifdef CRASH_DEBUG
 // crash_debug=y
 
-/* The main trap handlers use these helper macros which include early bail. */
-static inline int debugger_trap_entry(
-    unsigned int vector, struct cpu_user_regs *regs)
-{
-    return 0;
-}
-
 extern int __trap_to_cdb(struct cpu_user_regs *r);
 static inline int debugger_trap_fatal(
     unsigned int vector, struct cpu_user_regs *regs)
@@ -80,16 +73,7 @@
 #define smp_send_stop()	/* nothing */
 #endif
 
-#elif defined DOMU_DEBUG
-// domu_debug=y
-#warning "domu_debug is not implemented yet."
-/* The main trap handlers use these helper macros which include early bail. */
-static inline int debugger_trap_entry(
-    unsigned int vector, struct cpu_user_regs *regs)
-{
-    return 0;
-}
-
+#else
 static inline int debugger_trap_fatal(
     unsigned int vector, struct cpu_user_regs *regs)
 {
@@ -97,22 +81,21 @@
 }
 
 #define debugger_trap_immediate()		((void)0)
-#else
-/* The main trap handlers use these helper macros which include early bail. */
+#endif
+
 static inline int debugger_trap_entry(
     unsigned int vector, struct cpu_user_regs *regs)
 {
-    return 0;
-}
+    struct vcpu *v = current;
+
+    if (guest_kernel_mode(regs) && v->domain->debugger_attached) {
+        domain_pause_for_debugger();
+        return 1;
+    }
 
-static inline int debugger_trap_fatal(
-    unsigned int vector, struct cpu_user_regs *regs)
-{
     return 0;
 }
 
-#define debugger_trap_immediate()		((void)0)
-#endif
 #endif // __ASSEMBLLY__
 
 #endif /* __ASM_DEBUGGER_H__ */
--- xen/arch/ia64/xen/faults.c.gdbhang	2007-05-03 03:40:19.000000000 -0400
+++ xen/arch/ia64/xen/faults.c	2007-08-08 11:15:06.000000000 -0400
@@ -674,6 +674,11 @@
 		PSCB(current, iim) = iim;
 		vector = IA64_SPECULATION_VECTOR;
 		break;
+	case 29:
+		vector = IA64_DEBUG_VECTOR;
+		if (debugger_trap_entry(vector, regs))
+			return;
+		break;
 	case 30:
 		// FIXME: Should we handle unaligned refs in Xen??
 		vector = IA64_UNALIGNED_REF_VECTOR;
@@ -707,10 +712,14 @@
 	case 35:
 		printk("ia64_handle_reflection: handling taken branch trap\n");
 		vector = IA64_TAKEN_BRANCH_TRAP_VECTOR;
+		if (debugger_trap_entry(vector,regs))
+			return;
 		break;
 	case 36:
 		printk("ia64_handle_reflection: handling single step trap\n");
 		vector = IA64_SINGLE_STEP_TRAP_VECTOR;
+		if (debugger_trap_entry(vector,regs))
+			return;
 		break;
 
 	default: