Avi Kivity wrote:
> Jan Kiszka wrote:
>>> Maybe the backwards compatibility features should be ported to QEMU?
>>> For example, is there a workaround for
>>> #error Missing KVM capability KVM_CAP_DESTROY_MEMORY_REGION_WORKS
>>> ?
>>>     
>>
>> Given that we have always-up-to-date kvm-kmod packages with support down
>> to reasonable kernel versions, I would prefer to keep upstream clean
>> from old workarounds. They should only be needed for issues found very
>> recently (KVM_CAP_JOIN_MEMORY_REGIONS_WORKS) or that might be found in
>> the future.
>>   
> 
> Requiring the latest up-to-date modules is pushing the problem to the
> users.  Sometimes there is no choice, but when there is, the
> implementation that cares about its uses prefer unclean code and
> functionality over perfection and brokenness.

Let's make it more concrete:

By the time upstream is as well tested, feature-rich and with comparable
performance as qemu-kvm, its current baseline requirement (2.6.29 due to
KVM_CAP_DESTROY_MEMORY_REGION_WORKS) will no longer be a problem to most
normal users. Until then they are better off with qemu-kvm anyway.

So all I wanted to express is that I see no point in merging workarounds
upstream that hardly anyone will need but that restrict non-kvm code in
upstream. Basically I have the current line along
KVM_CAP_DESTROY_MEMORY_REGION_WORKS / clean memory slot management in
mind. Anything older should be skipped when merging upstream. And unless
something more problematic comes along (rather unlikely), 2.6.29 or
compatible kvm-kmod is a reasonable minimum requirement for the long term.

Jan