Re: [PATCH v2] KVM: x86: Extend KVM_SET_VCPU_EVENTS with selective updates

[Avi Kivity <avi@redhat.com>]

On 12/08/2009 04:02 PM, Marcelo Tosatti wrote:
> On Sun, Dec 06, 2009 at 06:24:15PM +0100, Jan Kiszka wrote:
>    
>> User space may not want to overwrite asynchronously changing VCPU event
>> states on write-back. So allow to skip nmi.pending and sipi_vector by
>> setting corresponding bits in the flags field of kvm_vcpu_events.
>>
>> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>>      
> Can't you handle this in userspace entirely, only updating vcpu_events
> state when appropriate?
>    

For what we do now I think you're right, it can be handled in userspace.

But in general, there's currently no way to update vcpu_events without 
overwriting nmi and sipi_vector, which can also be written concurrently 
by other vcpus.  So there's a hole in the interface.

> Shouldnt the vcpu be stopped in the first place, when its state is
> updated?
>    

It is stopped, but other vcpus are not.

-- 
error compiling committee.c: too many arguments to function