xen: add a handler for the debug interrupt

Handle the VIRQ_DEBUG signal and print a stack trace of each vCPU on the Xen
console. This is only used for debug purposes and is triggered by the
administrator of the Xen host.

Sponsored by: Citrix Systems R&D
MFC after: 1 week

1 files changed, 157 insertions, 0 deletions

diff --git a/sys/dev/xen/debug/debug.c b/sys/dev/xen/debug/debug.c
new file mode 100644
index 0000000..31bb709
--- /dev/null
+++ b/sys/dev/xen/debug/debug.c
@@ -0,0 +1,157 @@
+/*
+ * Copyright (c) 2015 Roger Pau Monné <roger.pau@citrix.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include "opt_stack.h"
+#include "opt_ddb.h"
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bus.h>
+#include <sys/kernel.h>
+#include <sys/module.h>
+#include <sys/pcpu.h>
+#include <sys/smp.h>
+#include <sys/stack.h>
+#include <sys/sbuf.h>
+
+#include <xen/xen-os.h>
+#include <xen/xen_intr.h>
+#include <xen/hypervisor.h>
+
+/*
+ * Xen debug device
+ *
+ * Handles the VIRQ_DEBUG interrupt and prints the backtrace of each
+ * vCPU on the Xen console.
+ */
+
+DPCPU_DEFINE(xen_intr_handle_t, xendebug_handler);
+static struct mtx lock;
+static struct sbuf *buf;
+
+static int
+xendebug_drain(void *arg, const char *str, int len)
+{
+
+	HYPERVISOR_console_write(__DECONST(char *, str), len);
+	return (len);
+}
+
+extern void
+stack_capture(struct stack *st, register_t rbp);
+
+static int
+xendebug_filter(void *arg)
+{
+#if defined(STACK) && defined(DDB)
+	struct stack st;
+	struct trapframe *frame;
+
+	frame = arg;
+	stack_zero(&st);
+	stack_save(&st);
+
+	mtx_lock_spin(&lock);
+	sbuf_clear(buf);
+	xc_printf("Printing stack trace vCPU%d\n", PCPU_GET(vcpu_id));
+	stack_sbuf_print_ddb(buf, &st);
+	sbuf_finish(buf);
+	mtx_unlock_spin(&lock);
+#endif
+
+	return (FILTER_HANDLED);
+}
+
+static void
+xendebug_identify(driver_t *driver, device_t parent)
+{
+
+	KASSERT(xen_domain(),
+	    ("Trying to add Xen debug device to non-xen guest"));
+
+	if (xen_hvm_domain() && !xen_vector_callback_enabled)
+		return;
+
+	if (BUS_ADD_CHILD(parent, 0, "debug", 0) == NULL)
+		panic("Unable to add Xen debug device.");
+}
+
+static int
+xendebug_probe(device_t dev)
+{
+
+	device_set_desc(dev, "Xen debug handler");
+	return (BUS_PROBE_NOWILDCARD);
+}
+
+static int
+xendebug_attach(device_t dev)
+{
+	int i, error;
+
+	mtx_init(&lock, "xen-dbg", NULL, MTX_SPIN);
+	buf = sbuf_new(NULL, NULL, 1024, SBUF_FIXEDLEN);
+	if (buf == NULL)
+		panic("Unable to create sbuf for stack dump");
+	sbuf_set_drain(buf, xendebug_drain, NULL);
+
+	/* Bind an event channel to a VIRQ on each VCPU. */
+	CPU_FOREACH(i) {
+		error = xen_intr_bind_virq(dev, VIRQ_DEBUG, i, xendebug_filter,
+		    NULL, NULL, INTR_TYPE_TTY,
+		    DPCPU_ID_PTR(i, xendebug_handler));
+		if (error != 0) {
+			printf("Failed to bind VIRQ_DEBUG to vCPU %d: %d",
+			    i, error);
+			continue;
+		}
+		xen_intr_describe(DPCPU_ID_GET(i, xendebug_handler), "d%d", i);
+	}
+
+	return (0);
+}
+
+static device_method_t xendebug_methods[] = {
+	DEVMETHOD(device_identify, xendebug_identify),
+	DEVMETHOD(device_probe, xendebug_probe),
+	DEVMETHOD(device_attach, xendebug_attach),
+
+	DEVMETHOD_END
+};
+
+static driver_t xendebug_driver = {
+	"debug",
+	xendebug_methods,
+	0,
+};
+
+devclass_t xendebug_devclass;
+
+DRIVER_MODULE(xendebug, xenpv, xendebug_driver, xendebug_devclass, 0, 0);
+MODULE_DEPEND(xendebug, xenpv, 1, 1, 1);