From fa884c14f16be6e13d68b98ed0ff66b78f0d48b4 Mon Sep 17 00:00:00 2001
From: Cornelia Huck <cornelia.huck@de.ibm.com>
Date: Fri, 14 Dec 2012 17:02:16 +0100
Subject: [PATCH] --- yaml --- r: 356796 b: refs/heads/master c:
 55c171a6d90dc0574021f9c836127cfd1a7d2e30 h: refs/heads/master v: v3

---
 [refs]                              |  2 +-
 trunk/drivers/s390/kvm/kvm_virtio.c | 38 +++++++++++++++++++++++------
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/[refs] b/[refs]
index eebffaa7718d..8e0bf126516a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d4b06c2d4cce466e2d62163c0a954e1b2ce96f8b
+refs/heads/master: 55c171a6d90dc0574021f9c836127cfd1a7d2e30
diff --git a/trunk/drivers/s390/kvm/kvm_virtio.c b/trunk/drivers/s390/kvm/kvm_virtio.c
index 7dabef624da3..b846b6c4130a 100644
--- a/trunk/drivers/s390/kvm/kvm_virtio.c
+++ b/trunk/drivers/s390/kvm/kvm_virtio.c
@@ -421,6 +421,26 @@ 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();