s390: PCI: fix IOMMU region init

The fix in dbe9cf606c shrinks the IOMMU memory region to a size
that seems reasonable on the surface, however is actually too
small as it is based against a 0-mapped address space.  This
causes breakage with small guests as they can overrun the IOMMU window.

Let's go back to the prior method of initializing iommu for now.

Fixes: dbe9cf606c ("s390x/pci: Set the iommu region size mpcifc request")
Cc: qemu-stable@nongnu.org
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Tested-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reported-by: Stefan Zimmerman <stzi@linux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Message-Id: <1569507036-15314-1-git-send-email-mjrosato@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

hw/s390x/s390-pci-bus.c

@@ -695,10 +695,15 @@ static const MemoryRegionOps s390_msi_ctrl_ops = {
 
 void s390_pci_iommu_enable(S390PCIIOMMU *iommu)
 {
+    /*
+     * The iommu region is initialized against a 0-mapped address space,
+     * so the smallest IOMMU region we can define runs from 0 to the end
+     * of the PCI address space.
+     */
     char *name = g_strdup_printf("iommu-s390-%04x", iommu->pbdev->uid);
     memory_region_init_iommu(&iommu->iommu_mr, sizeof(iommu->iommu_mr),
                              TYPE_S390_IOMMU_MEMORY_REGION, OBJECT(&iommu->mr),
-                             name, iommu->pal - iommu->pba + 1);
+                             name, iommu->pal + 1);
     iommu->enabled = true;
     memory_region_add_subregion(&iommu->mr, 0, MEMORY_REGION(&iommu->iommu_mr));
     g_free(name);