[qemu-s390x] [PATCH/RFC] s390x: split memory into 4TB chunks

[Christian Borntraeger]

KVM does not allow memory regions > KVM_MEM_MAX_NR_PAGES, basically
limiting the memory per slot to 7.999TB. Lets split the base memory
into 4TB chunks to allow go beyond 8TB for a guest. With that (and
optimistic overcommitment in the kernel) I was able to start  a 59TB
guest on a 1TB system.

Signed-off-by: Christian Borntraeger <address@hidden>
---
 hw/s390x/s390-virtio-ccw.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 8425534..6735bbb 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -157,11 +157,25 @@ static void virtio_ccw_register_hcalls(void)
 static void s390_memory_init(ram_addr_t mem_size)
 {
     MemoryRegion *sysmem = get_system_memory();
-    MemoryRegion *ram = g_new(MemoryRegion, 1);
+    ram_addr_t chunk, offset;
+    gchar *name;
 
     /* allocate RAM for core */
-    memory_region_allocate_system_memory(ram, NULL, "s390.ram", mem_size);
-    memory_region_add_subregion(sysmem, 0, ram);
+    offset = 0;
+    while (mem_size) {
+        MemoryRegion *ram = g_new(MemoryRegion, 1);
+        chunk = mem_size;
+        /* KVM does not allow memslots >= 8 TB. Lets split into 4TB chunks */
+        if (chunk > 4UL * 1024 * 1024 * 1024 * 1024) {
+            chunk = 4UL * 1024 * 1024 * 1024 * 1024;
+        }
+        name = g_strdup_printf("s390.ram[0x%lx]", offset);
+        memory_region_allocate_system_memory(ram, NULL, name, chunk);
+        memory_region_add_subregion(sysmem, offset, ram);
+        mem_size -= chunk;
+        offset += chunk;
+        g_free(name);
+    }
 
     /* Initialize storage key device */
     s390_skeys_init();
-- 
2.9.4