Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus

[Avi Kivity]

On 06/29/2009 01:06 PM, Michael S. Tsirkin wrote:
> > > 2. if I do it before in_range removal it's a lot of churn:
> > > one of the reasons for code reorg is so that there are less
> > > places to change locking.
> > >
> > >
> > >
> > >        
> > I don't think you really need to change anything.  slots_lock is already
> > taken (except where you modify the list).
> >      
>
> Are you sure about this? I don't understand the code well enough, so
> this reuse of an apparently unrelated lock just makes me nervious.  For
> example what about emulate_instruction? It is sometimes called from
> svm/vmx without slot lock ...
>    

vcpu context always has slots lock taken IIRC, except when in guest mode.

It's not an unrelated lock; slots lock locks memory hotplug, we extend 
it to lock mmio_bus and io_bus hotplug.

I'd really like to avoid a proliferation of locks.

> > How about this:
> >
> > 1. add slots_lock for write when modifying the list
> > 2. change the api
> > 3. drop kvm->lock
> >
> > ?
> >      
>
> Looks like I will just have to bite the bullet and switch to RCU.
>
>    

You still need a lock to prevent concurrent modifications to mmio_bus 
(but can use kvm->lock for this).


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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/