Re: [Xen-devel] [PATCH 4/8] x86/vm-event/monitor: turn monitor_write_data.do_write into enum

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

On 7/4/2016 3:37 PM, Jan Beulich wrote:
> > > > On 30.06.16 at 20:44, <czuzu@xxxxxxxxxxxxxxx> wrote:
> > After trapping a control-register write vm-event and -until- deciding if that
> > write is to be permitted or not (VM_EVENT_FLAG_DENY) and doing the actual
> > write,
> > there cannot and should not be another trapped control-register write event.
> Is that true even for the case where full register state gets updated
> for a vCPU?
AFAIK, the full register state cannot be updated _at once_, that is: 
after each trapped register update monitor_write_data must _always_ be 
handled _before reentering the vCPU_.
> Is that updating-all-context case of no interest to a
> monitoring application, now and forever?
As I said above, I'm don't see how such a case would (ever) be possible.

> > --- a/xen/include/asm-x86/domain.h
> > +++ b/xen/include/asm-x86/domain.h
> > @@ -259,19 +259,19 @@ struct pv_domain
> >       struct cpuidmasks *cpuidmasks;
> >   };
> >   
> > -struct monitor_write_data {
> > -    struct {
> > -        unsigned int msr : 1;
> > -        unsigned int cr0 : 1;
> > -        unsigned int cr3 : 1;
> > -        unsigned int cr4 : 1;
> > -    } do_write;
> > +enum monitor_write_status
> > +{
> > +    MWS_NOWRITE = 0,
> Please omit the "= 0" here - MWS_NOWRITE will be zero even
> without that.
>
> Jan
Ack.

Thanks,
Corneliu.

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