KVM: s390: Handle hosts not supporting s390-virtio.

Running under a kvm host does not necessarily imply the presence of
a page mapped above the main memory with the virtio information;
however, the code includes a hard coded access to that page.

Instead, check for the presence of the page and exit gracefully
before we hit an addressing exception if it does not exist.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
cc: stable@vger.kernel.org
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 30 insertions, 8 deletions

diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 7dabef624da3..b846b6c4130a 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -422,6 +422,26 @@ static void kvm_extint_handler(struct ext_code ext_code,
 }
 
 /*
+ * For s390-virtio, we expect a page above main storage containing
+ * the virtio configuration. Try to actually load from this area
+ * in order to figure out if the host provides this page.
+ */
+static int __init test_devices_support(unsigned long addr)
+{
+        int ret = -EIO;
+
+        asm volatile(
+                "0:     lura    0,%1\n"
+                "1:     xgr     %0,%0\n"
+                "2:\n"
+                EX_TABLE(0b,2b)
+                EX_TABLE(1b,2b)
+                : "+d" (ret)
+                : "a" (addr)
+                : "0", "cc");
+        return ret;
+}
+/*
  * Init function for virtio
  * devices are in a single page above top of "normal" mem
  */
@@ -432,21 +452,23 @@ static int __init kvm_devices_init(void)
         if (!MACHINE_IS_KVM)
                 return -ENODEV;
 
+        if (test_devices_support(real_memory_size) < 0)
+                return -ENODEV;
+
+        rc = vmem_add_mapping(real_memory_size, PAGE_SIZE);
+        if (rc)
+                return rc;
+
+        kvm_devices = (void *) real_memory_size;
+
         kvm_root = root_device_register("kvm_s390");
         if (IS_ERR(kvm_root)) {
                 rc = PTR_ERR(kvm_root);
                 printk(KERN_ERR "Could not register kvm_s390 root device");
+                vmem_remove_mapping(real_memory_size, PAGE_SIZE);
                 return rc;
         }
 
-        rc = vmem_add_mapping(real_memory_size, PAGE_SIZE);
-        if (rc) {
-                root_device_unregister(kvm_root);
-                return rc;
-        }
-
-        kvm_devices = (void *) real_memory_size;
-
         INIT_WORK(&hotplug_work, hotplug_devices);
 
         service_subclass_irq_register();