Commit bb223055 authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Cornelia Huck
Browse files

s390-ccw-virtio: allow for systems larger that 7.999TB 



KVM does not allow memory regions > KVM_MEM_MAX_NR_PAGES, basically
limiting the memory per slot to 8TB-4k. As memory slots on s390/kvm must
be a multiple of 1MB we need start a new memory region if we cross
8TB-1M.

With that (and optimistic overcommitment in the kernel) I was able to
start a 24TB guest on a 1TB system.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20171211122146.162430-1-borntraeger@de.ibm.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
[CH: 1UL -> 1ULL in KVM_MEM_MAX_NR_PAGES; build fix on 32 bit hosts]
Signed-off-by: default avatarCornelia Huck <cohuck@redhat.com>
parent 35b4df64

hw/s390x/s390-virtio-ccw.c

+27 −3
Original line number Diff line number Diff line
@@ -152,14 +152,38 @@ static void virtio_ccw_register_hcalls(void) 
                                   virtio_ccw_hcall_early_printk);

}



/*

 * KVM does only support memory slots up to KVM_MEM_MAX_NR_PAGES pages

 * as the dirty bitmap must be managed by bitops that take an int as

 * position indicator. If we have a guest beyond that we will split off

 * new subregions. The split must happen on a segment boundary (1MB).

 */

#define KVM_MEM_MAX_NR_PAGES ((1ULL << 31) - 1)

#define SEG_MSK (~0xfffffULL)

#define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) & SEG_MSK)

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 = 0;

    unsigned int number = 0;

    gchar *name;



    /* allocate RAM for core */

    memory_region_allocate_system_memory(ram, NULL, "s390.ram", mem_size);

    memory_region_add_subregion(sysmem, 0, ram);

    name = g_strdup_printf("s390.ram");

    while (mem_size) {

        MemoryRegion *ram = g_new(MemoryRegion, 1);

        uint64_t size = mem_size;



        /* KVM does not allow memslots >= 8 TB */

        chunk = MIN(size, KVM_SLOT_MAX_BYTES);

        memory_region_allocate_system_memory(ram, NULL, name, chunk);

        memory_region_add_subregion(sysmem, offset, ram);

        mem_size -= chunk;

        offset += chunk;

        g_free(name);

        name = g_strdup_printf("s390.ram.%u", ++number);

    }

    g_free(name);



    /* Initialize storage key device */

    s390_skeys_init();