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KVM: s390: Handle hosts not supporting s390-virtio.
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commit 55c171a upstream.

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>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Cornelia Huck authored and Greg Kroah-Hartman committed Feb 28, 2013
1 parent 8e78002 commit 25adbf9
Showing 1 changed file with 30 additions and 8 deletions.
38 changes: 30 additions & 8 deletions drivers/s390/kvm/kvm_virtio.c
Original file line number Diff line number Diff line change
Expand Up @@ -412,6 +412,26 @@ static void kvm_extint_handler(unsigned int ext_int_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
Expand All @@ -423,21 +443,23 @@ 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();
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