[Qemu-devel] [PATCH 1/4] s390/kvm: Handle hosts not supporting s390-virtio.

[Cornelia Huck]

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.

Signed-off-by: Cornelia Huck <address@hidden>
---
 drivers/s390/kvm/kvm_virtio.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 47cccd5..408447c 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -418,6 +418,21 @@ static void kvm_extint_handler(struct ext_code ext_code,
        }
 }
 
+static int __init test_devices_support(void)
+{
+       int ccode = -EIO;
+
+       asm volatile(
+               "0:     cli     0(%1),0\n"
+               "       ipm     %0\n"
+               "       srl     %0,28\n"
+               "1:\n"
+               EX_TABLE(0b,1b)
+               : "+d" (ccode)
+               : "a" (kvm_devices)
+               : "cc");
+       return ccode;
+}
 /*
  * Init function for virtio
  * devices are in a single page above top of "normal" mem
@@ -443,6 +458,12 @@ static int __init kvm_devices_init(void)
        }
 
        kvm_devices = (void *) real_memory_size;
+       if (test_devices_support() < 0) {
+               vmem_remove_mapping(real_memory_size, PAGE_SIZE);
+               root_device_unregister(kvm_root);
+               /* No error. */
+               return 0;
+       }
 
        INIT_WORK(&hotplug_work, hotplug_devices);
 
-- 
1.7.11.4