Re: [Xen-devel] [PATCH 1/2] xen/arm: support the ARM generic virtual timer

[Tim Deegan <tim@xxxxxxx>]

At 11:46 +0000 on 14 Feb (1360842373), Stefano Stabellini wrote:
> On Thu, 24 Jan 2013, Tim Deegan wrote:
> > At 16:17 +0000 on 09 Jan (1357748277), Stefano Stabellini wrote:
> > > +static void vtimer_interrupt(int irq, void *dev_id, struct cpu_user_regs 
> > > *regs)
> > > +{
> > > +    current->arch.virt_timer.ctl = READ_CP32(CNTV_CTL);
> > > +    WRITE_CP32(current->arch.virt_timer.ctl | CNTx_CTL_MASK, CNTV_CTL);
> > 
> > This is masking the vtimer interrupt in a way that's visible to the
> > currently running guest.  Is that going to confuse the guest?
> >
> > When we talked about this before I had imagined that the masking would
> > happen in the GIC, where the guest doesn't see it. 
> 
> I know it is not ideal but it is safe, it is not creating any problems to
> Linux and it is even the same thing that KVM does).

Grrr.  So it's safe unless you run something other than linux, or KVM
devs change their minds...

Do we have an interface document to describe the PV machine that we
provide to a guest?  If so, this divergence from the spec should be
described there.  If not, we really should. :)

Tim.

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