Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> Sent: 17 February 2016 09:58
> To: Paul Durrant; Jan Beulich
> Cc: Andrew Cooper; George Dunlap; Ian Campbell; Ian Jackson; Stefano
> Stabellini; Wei Liu; Lv, Zhiyuan; Zhang Yu; xen-devel@xxxxxxxxxxxxx; George
> Dunlap; Keir (Xen.org)
> Subject: RE: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter
> max_wp_ram_ranges.
> 
> > From: Paul Durrant [mailto:Paul.Durrant@xxxxxxxxxx]
> > Sent: Wednesday, February 17, 2016 4:58 PM
> >
> > >
> > > btw does this design consider the case where multiple ioreq servers
> > > may claim on same page?
> >
> > Yes it does and there are currently insufficient page types to allow any
> more than a single
> > ioreq server to claim a type. My plan is that, in future, we can add a p2t
> mapping table to
> > allow for more types and then introduce HVMMEM_ioreq_1,
> HVMMEM_ioreq_2, etc.
> 
> so these new types actually represent ioreq server ID, right? If yes I can 
> then
> understand your earlier explanations.

Well, not quite. Each of these types can be steered to exactly one ioreq server 
but there will be a new hypercall to control the mapping. The design doc will 
make it clear.

  Paul

> 
> >
> > > For example, different usages may both
> > > want to capture write requests on the same set of pages (say XenGT
> > > selectively write-protects a subset of pages due to shadow GTT, while
> > > another agent wants to monitor all guest writes to any guest memory
> > > page).
> >
> > Monitoring is a different thing altogether. Emulation is costly and not
> something you'd want
> > to use for that purpose. If you want to monitor writes then log-dirty
> already exists for that
> > purpose.
> 
> Agree.
> 
> >
> > >
> > > Thanks
> > > Kevin
> >
> > I hope my explanation helped. I think things will be clearer once I've had
> chance to actually
> > put together a design doc. and hack up a PoC (probably only for EPT at
> first).
> >
> 
> Thanks for the help. Let's see whether we can have some solution ready for
> 4.7. :-)
> 
> Thanks
> Kevin

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