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

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

Am 26/08/2022 um 16:44 schrieb 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?

I am going to send it today. I got something working, but it's a little
bit messy on the invalid slots part.

> 
> 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.
> 
> 

Limiting the size of operations in the IOCTL can be something for the
future. Currently it's already pretty complicated as it is (in the KVM
side), plus I don't see ioctls with more than 8 requests.

Thank you,
Emanuele