Drivers: hv: avoid vfree() on crash

commit a9f61ca7 upstream.

When we crash from NMI context (e.g. after NMI injection from host when
'sysctl -w kernel.unknown_nmi_panic=1' is set) we hit

    kernel BUG at mm/vmalloc.c:1530!

as vfree() is denied. While the issue could be solved with in_nmi() check
instead I opted for skipping vfree on all sorts of crashes to reduce the
amount of work which can cause consequent crashes. We don't really need to
free anything on crash.

[js] no tsc and kexec in 3.12 yet
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/hv/hv.c

@@ -193,7 +193,7 @@ int hv_init(void)
  *
  * This routine is called normally during driver unloading or exiting.
  */
-void hv_cleanup(void)
+void hv_cleanup(bool crash)
 {
 	union hv_x64_msr_hypercall_contents hypercall_msr;
 
@@ -203,7 +203,8 @@ void hv_cleanup(void)
 	if (hv_context.hypercall_page) {
 		hypercall_msr.as_uint64 = 0;
 		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
-		vfree(hv_context.hypercall_page);
+		if (!crash)
+			vfree(hv_context.hypercall_page);
 		hv_context.hypercall_page = NULL;
 	}
 }

drivers/hv/hyperv_vmbus.h

@@ -519,7 +519,7 @@ extern struct hv_context hv_context;
 
 extern int hv_init(void);
 
-extern void hv_cleanup(void);
+extern void hv_cleanup(bool crash);
 
 extern int hv_post_message(union hv_connection_id connection_id,
 			 enum hv_message_type message_type,

drivers/hv/vmbus_drv.c

@@ -622,7 +622,7 @@ static int vmbus_bus_init(int irq)
 	bus_unregister(&hv_bus);
 
 err_cleanup:
-	hv_cleanup();
+	hv_cleanup(false);
 
 	return ret;
 }
@@ -845,7 +845,7 @@ static void __exit vmbus_exit(void)
 	free_irq(irq, hv_acpi_dev);
 	vmbus_free_channels();
 	bus_unregister(&hv_bus);
-	hv_cleanup();
+	hv_cleanup(false);
 	acpi_bus_unregister_driver(&vmbus_acpi_driver);
 	hv_cpu_hotplug_quirk(false);
 }