Re: [Qemu-devel] [PATCH v2 1/8] kvm: Set cpu_single_env only once

[Blue Swirl]

On Sat, Feb 11, 2012 at 14:00, Jan Kiszka <address@hidden> wrote:
> On 2012-02-11 14:54, Blue Swirl wrote:
>> On Sat, Feb 11, 2012 at 12:43, Jan Kiszka <address@hidden> wrote:
>>> On 2012-02-11 12:49, Andreas Färber wrote:
>>>> Am 11.02.2012 12:25, schrieb Blue Swirl:
>>>>> I think using cpu_single_env is an indication of a problem, like poor
>>>>> code, layering violation or poor API (vmport). What is your use case?
>>>>
>>>> I couldn't spot any in this series. Jan, note that any new use of env or
>>>> cpu_single_env will need to be redone when we convert to QOM CPU.
>>>
>>> cpu_single_env should have nothing to do with QOM.
>>>
>>> The ABIs of vmport and the KVM VAPI require a reference to the calling
>>> VCPU, and that's why you find tons of them in patch 5.
>>
>> Yes, this seems to be another case of a badly designed ABI. I guess
>> there is no way to change that anymore, just like vmport?
>
> Believe me, I grumbled over it more than once while porting it from
> qemu-kvm. The point is that some (Windows) VMs out there are running
> already with this option ROM loaded and working this unfortunate ABI.

Maybe in time those could be deprecated and a ROM using a sane ABI
introduced instead. After some grace time the old ABI could be finally
removed.

>>
>> Some of the cpu_single_env accesses in patch 5 could be avoided when
>> APIC is moved closer to CPU. VAPIC should be also close to APIC so it
>> should be able to access the CPU directly. In some other cases the
>> current state could be passed around instead once it is known.
>
> Some callbacks are I/O-port originated, ie. not associated with the
> per-CPU MMIO area or some MSR. So we would have to pass down the causing
> CPU to every I/O handler - not sure if that is desired...

I meant things like vapic_enable_tpr_reporting(), current CPUState
could be passed via vapic_prepare() easily.

> Jan
>