Re: [PATCH 0/7] Consolidate vcpu ioctl locking

Am 13.05.2010 um 14:29 schrieb Avi Kivity <[email protected]>:

> On 05/13/2010 03:18 PM, Alexander Graf wrote:
>>
>>> [PATCH 0/7] Consolidate vcpu ioctl locking
>>>
>>> In general, all vcpu ioctls need to take the vcpu mutex, but each  
>>> one does it
>>> (or not) individually.  This is cumbersome and error prone.
>>>
>>> This patchset moves all locking to a central place.  This is  
>>> complicated
>>> by the fact that ppc's KVM_INTERRUPT and s390's KVM_S390_INTERRUPT  
>>> break
>>> the convention and need to run unlocked.
>>>
>> Why is the x86 non-kernel-pic path different?
>>
>
> Userspace issues the ioctl from a vcpu thread.
>
> It has to, btw, since whether an interrupt can be injected or not  
> depends on vcpu-synchronous registers: eflags.if and tpr/cr8.

On ppc we don't have a tpr, but eflags.if is basically the same as  
msr.ee.

The major difference apparently is that on ppc we KVM_INTERRUPT pulls  
the interrupt line. On vcpu_run we then check whether msr.ee is set  
and if so, trigger the interrupt.

I wonder why we don't do the same for x86. The current limitation on  
userspace checking eflags and the tpr seems cumbersome.

Alex

>