On 12/11/2017 02:55 PM, David Hildenbrand wrote:
> On 11.12.2017 13:21, Christian Borntraeger wrote:
>> 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: Christian Borntraeger <borntrae...@de.ibm.com>
>> ---
>> hw/s390x/s390-virtio-ccw.c | 28 +++++++++++++++++++++++++---
>> 1 file changed, 25 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index 8425534..073f6ed 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -154,14 +154,36 @@ 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 ((1UL << 31) - 1)
>> +#define SEG_MSK (~0xfffffULL)
>> +#define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) &
>> SEG_MSK)
>
> Just wondering if we could get into trouble when calculating
>
> KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE
maybe just using 1ULL instead of 1UL?
>
> on a host with sizeof(long) == 4
>
> could it wrap? (e.g. crazy mingw stuff)
>
>> 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);
>
> I'd add an empty line here.
>
> Reviewed-by: David Hildenbrand <da...@redhat.com>
>
>> + /* KVM does not allow memslots >= 8 TB */
>> + chunk = MIN(mem_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();
>>
>
>
