pv-on-hvm: Signal crash to Xen tools when HVM guest panics.

Attached patch adds a function to automatically dump core file when
guest linux on HVM domain panics, in the same way as PV domain.

I tested this patch with kernel 2.6.9 and 2.6.18 on both of x86 and
ia64 (to buid for ia64, some patches in the ia64 tree are needed) by
the following steps, and confirmed it works well:

1. Build xen-platform-pci.ko.
2. In /etc/xen/xend-config.sxp, set (enable-dump yes).
3. On guest linux, execute insmod:
   # insmod xen-platform-pci.ko
4. When guest linux panics, a core file is dumped.

Signed-off-by: Tetsu Yamamoto <yamamoto.tetsu@jp.fujitsu.com>

unmodified_drivers/linux-2.6/platform-pci/Kbuild

@@ -7,6 +7,7 @@ EXTRA_CFLAGS += -I$(M)/platform-pci
 xen-platform-pci-objs := evtchn.o platform-pci.o gnttab.o xen_support.o
 xen-platform-pci-objs += features.o platform-compat.o
 xen-platform-pci-objs += reboot.o machine_reboot.o
+xen-platform-pci-objs += panic-handler.o
 
 xen-platform-pci-objs += ../xenbus/xenbus_comms.o
 xen-platform-pci-objs += ../xenbus/xenbus_xs.o

unmodified_drivers/linux-2.6/platform-pci/panic-handler.c

@@ -0,0 +1,54 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <asm/hypervisor.h>
+
+MODULE_LICENSE("GPL");
+
+#ifdef __ia64__
+static void
+xen_panic_hypercall(struct unw_frame_info *info, void *arg)
+{
+	current->thread.ksp = (__u64)info->sw - 16;
+	HYPERVISOR_shutdown(SHUTDOWN_crash);
+	/* we're never actually going to get here... */
+}
+#endif
+
+static int
+xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr)
+{
+#ifdef __ia64__
+	unw_init_running(xen_panic_hypercall, NULL);
+#else /* !__ia64__ */
+	HYPERVISOR_shutdown(SHUTDOWN_crash);
+#endif
+	/* we're never actually going to get here... */
+	return NOTIFY_DONE;
+}
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18)
+static struct notifier_block xen_panic_block = {
+	xen_panic_event, NULL, 0 /* try to go last */
+};
+#else
+static struct notifier_block xen_panic_block = {
+	.notifier_call= xen_panic_event,
+	.next= NULL,
+	.priority= 0/* try to go last */
+};
+#endif /*LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18)*/
+
+static int __init setup_panic_event(void)
+{
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18)
+	notifier_chain_register(&panic_notifier_list, &xen_panic_block);
+#else
+	atomic_notifier_chain_register(&panic_notifier_list, &xen_panic_block);
+#endif /*LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18)*/
+	return 0;
+}
+
+int xen_panic_handler_init(void)
+{
+	return setup_panic_event();
+}

unmodified_drivers/linux-2.6/platform-pci/platform-pci.c

@@ -249,6 +249,7 @@ static int set_callback_via(uint64_t via)
 int xen_irq_init(struct pci_dev *pdev);
 int xenbus_init(void);
 int xen_reboot_init(void);
+int xen_panic_handler_init(void);
 int gnttab_init(void);
 
 static int __devinit platform_pci_init(struct pci_dev *pdev,
@@ -317,6 +318,9 @@ static int __devinit platform_pci_init(struct pci_dev *pdev,
 	if ((ret = xen_reboot_init()))
 		goto out;
 
+	if ((ret = xen_panic_handler_init()))
+		goto out;
+
  out:
 	if (ret) {
 		release_mem_region(mmio_addr, mmio_len);