Re: [Xen-devel] [PATCH v7] x86/emulate: Send vm_event from emulate

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 7/19/19 4:18 PM, Jan Beulich wrote:
> On 19.07.2019 14:34, Alexandru Stefan ISAILA wrote:
> > On 18.07.2019 15:58, Jan Beulich wrote:
> > > On 03.07.2019 12:56, Alexandru Stefan ISAILA wrote:
> > > > A/D bit writes (on page walks) can be considered benign by an introspection
> > > > agent, so receiving vm_events for them is a pessimization. We try here to
> > > > optimize by fitering these events out.
> > > But you add the sending of more events - how does "filter out" match
> > > the actual implementation?
> > The events are send only if there is a mem access violation therefore we
> > are filtering and only sending the events that are interesting to
> > introspection.
> Where is it that you prevent any event from being sent? As said,
> reading the patch I only see new sending sites to get added.
If we don't emulate, we would receive the page-walk-generated events 
_and_ the touching-the-page-the-instruction-is-touching events.
In comparison to the "hardware" case, the case where we emulate the 
instruction with the page walk ignoring the EPT results in less events, 
hence the prevention of some events being sent out.

Thanks,
Razvan

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