Re: [Xen-devel] [PATCH 3/5] x86/hvm: Make HVM_PARAM_{STORE, CONSOLE}_EVTCHN read-only to the guest

[Julien Grall <julien.grall@xxxxxxx>]

On 06/09/18 16:29, Andrew Cooper wrote:
> On 06/09/18 10:16, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> > > Sent: 05 September 2018 19:12
> > > To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> > > Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
> > > <JBeulich@xxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Roger Pau Monne
> > > <roger.pau@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Stefano
> > > Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>
> > > Subject: [PATCH 3/5] x86/hvm: Make
> > > HVM_PARAM_{STORE,CONSOLE}_EVTCHN read-only to the guest
> > >
> > > These values are set by the toolstack for each create/restore operation, and
> > > bound by xen{store,console}d before the the guest starts running.
> > >
> > > A guest has no reason to modify them at all, and the matching *_PFN
> > > parameters
> > > are already read-only.  Adjust the *_EVTCHN permissions to be consistent.
> > Unfortunately this patch will break the Windows PV driver function here:
> >
> > http://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenbus.git;a=blob;f=src/xenbus/evtchn.c;hb=HEAD#l1037
> >
> > Unfortunately the values really do change across a reset. It would be possible 
> > to use volatile (disappear on reboot) registry keys to store the updated values 
> > instead but I don't really see any harm in allowing the guest to update the 
> > values to be correct, unless we want to change Xen to do the job so the guest 
> > doesn't have to go through this dance.
> :(  Everything is terrible.
>
> This is a general problem, not x86 specific, so I'll drop this patch and
> make a similar adjustment to the ARM one.
I am a bit confused. I would have thought this was updated by the 
toolstack at reset. So why would the guest update them?
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel