Drivers: hv: vmbus: add special crash handler

Full kernel hang is observed when kdump kernel starts after a crash. This
hang happens in vmbus_negotiate_version() function on
wait_for_completion() as Hyper-V host (Win2012R2 in my testing) never
responds to CHANNELMSG_INITIATE_CONTACT as it thinks the connection is
already established. We need to perform some mandatory minimalistic
cleanup before we start new kernel.
Reported-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/mshyperv.h

@@ -22,4 +22,6 @@ void hv_remove_vmbus_irq(void);
 
 void hv_setup_kexec_handler(void (*handler)(void));
 void hv_remove_kexec_handler(void);
+void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs));
+void hv_remove_crash_handler(void);
 #endif

arch/x86/kernel/cpu/mshyperv.c

@@ -35,6 +35,7 @@ struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);
 
 static void (*hv_kexec_handler)(void);
+static void (*hv_crash_handler)(struct pt_regs *regs);
 
 #if IS_ENABLED(CONFIG_HYPERV)
 static void (*vmbus_handler)(void);
@@ -83,6 +84,18 @@ void hv_remove_kexec_handler(void)
 	hv_kexec_handler = NULL;
 }
 EXPORT_SYMBOL_GPL(hv_remove_kexec_handler);
+
+void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs))
+{
+	hv_crash_handler = handler;
+}
+EXPORT_SYMBOL_GPL(hv_setup_crash_handler);
+
+void hv_remove_crash_handler(void)
+{
+	hv_crash_handler = NULL;
+}
+EXPORT_SYMBOL_GPL(hv_remove_crash_handler);
 #endif
 
 static void hv_machine_shutdown(void)
@@ -92,6 +105,14 @@ static void hv_machine_shutdown(void)
 	native_machine_shutdown();
 }
 
+static void hv_machine_crash_shutdown(struct pt_regs *regs)
+{
+	if (hv_crash_handler)
+		hv_crash_handler(regs);
+	native_machine_crash_shutdown(regs);
+}
+
+
 static uint32_t  __init ms_hyperv_platform(void)
 {
 	u32 eax;
@@ -165,6 +186,7 @@ static void __init ms_hyperv_init_platform(void)
 #endif
 
 	machine_ops.shutdown = hv_machine_shutdown;
+	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {

drivers/hv/vmbus_drv.c

@@ -1071,6 +1071,18 @@ static void hv_kexec_handler(void)
 	hv_cleanup();
 };
 
+static void hv_crash_handler(struct pt_regs *regs)
+{
+	vmbus_initiate_unload();
+	/*
+	 * In crash handler we can't schedule synic cleanup for all CPUs,
+	 * doing the cleanup for current CPU only. This should be sufficient
+	 * for kdump.
+	 */
+	hv_synic_cleanup(NULL);
+	hv_cleanup();
+};
+
 static int __init hv_acpi_init(void)
 {
 	int ret, t;
@@ -1104,6 +1116,7 @@ static int __init hv_acpi_init(void)
 		goto cleanup;
 
 	hv_setup_kexec_handler(hv_kexec_handler);
+	hv_setup_crash_handler(hv_crash_handler);
 
 	return 0;
 
@@ -1118,6 +1131,7 @@ static void __exit vmbus_exit(void)
 	int cpu;
 
 	hv_remove_kexec_handler();
+	hv_remove_crash_handler();
 	vmbus_connection.conn_state = DISCONNECTED;
 	hv_synic_clockevents_cleanup();
 	vmbus_disconnect();