[PATCH v1 01/14] s390x/s390-virtio-ccw: don't crash on weird RAM sizes

[David Hildenbrand <david@redhat.com>]

KVM is not happy when starting a VM with weird RAM sizes:

  # qemu-system-s390x --enable-kvm --nographic -m 1234K
  qemu-system-s390x: kvm_set_user_memory_region: KVM_SET_USER_MEMORY_REGION
    failed, slot=0, start=0x0, size=0x244000: Invalid argument
  kvm_set_phys_mem: error registering slot: Invalid argument
  Aborted (core dumped)

Let's handle that in a better way by rejecting such weird RAM sizes
right from the start:

  # qemu-system-s390x --enable-kvm --nographic -m 1234K
  qemu-system-s390x: ram size must be multiples of 1 MiB

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/s390x/s390-virtio-ccw.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 18240a0fd8..e30cf0a2a1 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -180,6 +180,17 @@ static void s390_memory_init(MemoryRegion *ram)
 {
     MemoryRegion *sysmem = get_system_memory();
 
+    if (!QEMU_IS_ALIGNED(memory_region_size(ram), 1 * MiB)) {
+        /*
+         * The SCLP cannot possibly expose smaller granularity right now and KVM
+         * cannot handle smaller granularity. As we don't support NUMA, the
+         * region size directly corresponds to machine->ram_size, and the region
+         * is a single RAM memory region.
+         */
+        error_report("ram size must be multiples of 1 MiB");
+        exit(EXIT_FAILURE);
+    }
+
     /* allocate RAM for core */
     memory_region_add_subregion(sysmem, 0, ram);
 
-- 
2.46.0