Re: [RFC PATCH 2/2] kvm/kvm-all.c: listener should delay kvm_vm_ioctl to the commit phase

[David Hildenbrand]

On 26.08.22 16:32, Emanuele Giuseppe Esposito wrote:
> 
> 
> Am 26/08/2022 um 16:15 schrieb David Hildenbrand:
>> On 16.08.22 12:12, Emanuele Giuseppe Esposito wrote:
>>> Instead of sending a single ioctl every time ->region_* or ->log_*
>>> callbacks are called, "queue" all memory regions in a list that will
>>> be emptied only when committing.
>>>
>>
>> Out of interest, how many such regions does the ioctl support? As many
>> as KVM theoretically supports? (32k IIRC)
>>
> 
> I assume you mean for the new ioctl, but yes that's a good question.
> 
> The problem here is that we could have more than a single update per
> memory region. So we are not limited anymore to the number of regions,
> but the number of operations * number of region.
> 
> I was thinking, maybe when pre-processing QEMU could divide a single
> transaction into multiple atomic operations (ie operations on the same
> memory region)? That way avoid sending a single ioctl with 32k *
> #operation elements. Is that what you mean?

Oh, so we're effectively collecting slot updates and not the complete
"slot" view, got it. Was the kernel series already sent so I can have a
look?

Note that there are some possible slot updates (like a split, or a
merge) that involve multiple slots and that would have to be part of the
same "transaction" to be atomic.


-- 
Thanks,

David / dhildenb