[Stable-9.2.1,11/41] s390x/s390-virtio-ccw: don't crash on weird RAM sizes

Commit Message

Michael Tokarev Jan. 27, 2025, 2:17 p.m. UTC

From: David Hildenbrand <[e-mail]>

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

Message-ID: <[e-mail]>
Acked-by: Michael S. Tsirkin <[e-mail]>
Reviewed-by: Eric Farman <[e-mail]>
Reviewed-by: Thomas Huth <[e-mail]>
Acked-by: Janosch Frank <[e-mail]>
Signed-off-by: David Hildenbrand <[e-mail]>
(cherry picked from commit 14e568ab4836347481af2e334009c385f456a734)
Signed-off-by: Michael Tokarev <[e-mail]>

Patch

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index fe03f716f3..53c62fb77c 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)) {
+        /*
+         * 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);