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 4:07 PM, Jan Beulich wrote:
> > > > On 04.07.16 at 14:47, <czuzu@xxxxxxxxxxxxxxx> wrote:
> > 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_.
> I'm thinking about operations like VCPUOP_initialise here. Of course
> operations on current can't possibly update more than one register
> at a time.
>
> Jan
Yes but those register update operations happen outside the vm-event 
subsystem, i.e. in those cases the registers get updated directly, not 
by setting bits in monitor_write_data.
Only hypervisor-trapped register updates (e.g. hvm_set_cr0 w/ may_defer 
parameter = 1) which are deferred because of hvm_event_crX returning 
true use monitor_write_data.
Corneliu.

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