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

[Christian Borntraeger]

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?