Re: [RFC PATCH 1/6] kvm: add device control API

[Scott Wood <scottwood@freescale.com>]

On 02/20/2013 06:14:37 PM, Marcelo Tosatti wrote:
> On Wed, Feb 20, 2013 at 05:53:20PM -0600, Scott Wood wrote:
> > >It is then not necessary to set device attributes on a live guest  
> and
> > >deal with the complications associated with that.
> >
> > Which complications?
> >
> > -Scott
> 
> Semantics of individual attribute writes, for one.

When the attribute is a device register, the hardware documentation  
takes care of that.  Otherwise, the semantics are documented in the  
device-specific documentation -- which can include restricting when the  
access is allowed.  Same as with any other interface documentation.

I suppose mpic.txt could use an additional statement that  
KVM_DEV_MPIC_GRP_REGISTER performs an access as if it were performed by  
the guest.

> Locking versus currently executing VCPUs, for another (see how
> KVM_SET_IRQ's RCU usage, for instance, that is something should be
> shared).

If you mean kvm_set_irq() in irq_comm.c, that's only relevant when you  
have a GSI routing table, which this patchset doesn't.

Assuming we end up having a routing table to support irqfd, we still  
can't share the code as is, since it's APIC-specific.

-Scott