Re: [Xen-devel] [PATCH v2 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Yu, Zhang [mailto:yu.c.zhang@xxxxxxxxxxxxxxx]
> Sent: Thursday, April 14, 2016 5:57 PM
> >>>>> And with all three bits now possibly being clear, aren't we risking the
> >>>>> entries to be mis-treated as not-present ones?
> >>>>
> >>>> Hah. You got me. Thanks! :)
> >>>> Now I realized it would be difficult if we wanna to emulate the read
> >>>> operations for HVM. According to Intel mannual, entry->r is to be
> >>>> cleared, so should entry->w if we do not want ept misconfig. And
> >>>> with both read and write permissions being forbidden, entry->x can be
> >>>> set only on processors with EXECUTE_ONLY capability.
> >>>> To avoid any entry to be mis-treated as not-present. We have several
> >>>> solutions:
> >>>> a> do not support the read emulation for now - we have no such usage
> >>>> case;
> >>>> b> add the check of p2m_t against p2m_ioreq_server in is_epte_present -
> >>>> a bit weird to me.
> >>>> Which one do you prefer? or any other suggestions?
> >>>
> >>> That question would also need to be asked to others who had
> >>> suggested supporting both. I'd be fine with a, but I also don't view
> >>> b as too awkward.
> >>
> >> According to Intel mannual, an entry is regarded as not present, if
> >> bit0:2 is 0. So adding a p2m type check in is_epte_present() means we
> >> will change its semantics, if this is acceptable(with no hurt to
> >> hypervisor). I'd prefer option b>
> >
> > Perhaps time for the VMX maintainers to chime in - such a change is 
> > acceptable
> > only if it doesn't result in changed hardware behavior. I can't think of 
> > any such off
> > the top of my head, but this really should be confirmed by the maintainers 
> > before
> > deciding to go such a route.
> >
> 
> Thanks, Jan. :)
> Jun & Kevin, any suggestions?
> 

I'm a bit worried about this change, since it's a fundamental EPT
interface. Can we avoid supporting read emulation now?

Thanks
Kevin

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel