Re: [qemu-s390x] [PATCH for-4.2 v5 1/2] kvm: s390: split too big memory section on several memslots

[Christian Borntraeger]

On 29.08.19 14:04, Igor Mammedov wrote:
> On Thu, 29 Aug 2019 08:47:49 +0200
> Christian Borntraeger <address@hidden> wrote:
> 
>> On 27.08.19 14:56, Igor Mammedov wrote:
>>> On Tue, 20 Aug 2019 18:07:27 +0200
>>> Cornelia Huck <address@hidden> wrote:
>>>   
>>>> On Wed,  7 Aug 2019 11:32:41 -0400
>>>> Igor Mammedov <address@hidden> wrote:
>>>>  
>>>>> Max memslot size supported by kvm on s390 is 8Tb,
>>>>> move logic of splitting RAM in chunks upto 8T to KVM code.
>>>>>
>>>>> This way it will hide KVM specific restrictions in KVM code
>>>>> and won't affect baord level design decisions. Which would allow
>>>>> us to avoid misusing memory_region_allocate_system_memory() API
>>>>> and eventually use a single hostmem backend for guest RAM.
>>>>>
>>>>> Signed-off-by: Igor Mammedov <address@hidden>
>>>>> ---
>>>>> v5:
>>>>>   * move computation 'size -= slot_size' inside of loop body
>>>>>           (David Hildenbrand <address@hidden>)
>>>>> v4:
>>>>>   * fix compilation issue
>>>>>           (Christian Borntraeger <address@hidden>)
>>>>>   * advance HVA along with GPA in kvm_set_phys_mem()
>>>>>           (Christian Borntraeger <address@hidden>)
>>>>>
>>>>> patch prepares only KVM side for switching to single RAM memory region
>>>>> another patch will take care of  dropping manual RAM partitioning in
>>>>> s390 code.    
>>>>
>>>> I may have lost track a bit -- what is the status of this patch (and
>>>> the series)?  
>>>
>>> Christian,
>>>
>>> could you test it on a host that have sufficient amount of RAM?  
>>
>>
>> This version looks good. I was able to start a 9TB guest.
>> [pid 215723] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=0, flags=0, 
>> guest_phys_addr=0, memory_size=8796091973632, userspace_addr=0x3ffee700000}) 
>> = 0
>> [pid 215723] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=1, flags=0, 
>> guest_phys_addr=0x7fffff00000, memory_size=1099512676352, 
>> userspace_addr=0xbffee600000}) = 0
>>
>> The only question is if we want to fix the weird alignment (0x7fffff00000) 
>> when
>> we already add a migration barrier for uber-large guests.
>> Maybe we could split at 4TB to avoid future problem with larger page sizes?
> That probably should be a separate patch on top.

Right. The split in KVM code is transparent to migration and other parts of 
QEMU, correct?