On Jan 28, 2016 8:02 AM, "Razvan Cojocaru" <rcojoc...@bitdefender.com> wrote: > > On 01/28/2016 04:42 PM, Lengyel, Tamas wrote: > > > > On Jan 28, 2016 6:38 AM, "Jan Beulich" <jbeul...@suse.com > > <mailto:jbeul...@suse.com>> wrote: > >> > >> >>> On 27.01.16 at 21:06, <tleng...@novetta.com > > <mailto:tleng...@novetta.com>> wrote: > >> > --- a/xen/arch/x86/mm/p2m.c > >> > +++ b/xen/arch/x86/mm/p2m.c > >> > @@ -1572,7 +1572,9 @@ void p2m_mem_access_emulate_check(struct vcpu *v, > >> > bool_t violation = 1; > >> > const struct vm_event_mem_access *data = &rsp->u.mem_access; > >> > > >> > - if ( p2m_get_mem_access(v->domain, _gfn(data->gfn), > > &access) == 0 ) > >> > + if ( p2m_get_mem_access(v->domain, _gfn(data->gfn), > >> > + altp2m_active(v->domain) ? > > vcpu_altp2m(v).p2midx : 0, > >> > + &access) == 0 ) > >> > >> This looks to be a behavioral change beyond what title and > >> description say, and it's not clear whether that's actually the > >> behavior everyone wants. > > > > I'm fairly comfident its exactly the expected behavior when one uses > > mem_access in altp2m tables and emulation. Right now because the lack of > > this AFAIK emulation would not work correctly with altp2m. But Razvan > > probably can chime in as he uses this path actively. > > I've done an experiment to see how much slower using altp2m would be as > compared to emulation - so I'm not a big user of the feature, but I did > find it cumbersome to have to work with two sets of APIs (one for what > could arguably be called the default altp2m view, i.e. the regular > xc_set_mem_access(), and one for altp2m, i.e. > xc_altp2m_set_mem_access()). Furthermore, the APIs do not currently > offer the same features (most notably, xc_altp2m_get_mem_access() is > completely missing). I've mentioned this to Tamas while initially trying > to get it to work. > > Now, whether the behaviour I expect is what everyone expects is, of > course, wide open to debate. But I think we can all agree that the > altp2m interface can, and probably should, be improved. >
There is that, but also, what is the exact logic behind doing this check before emulation? AFAIU emulation happens in response to a vm_event so we should be fairly certain that this check succeeds as it just verifies that indeed the permissions are restricted by mem_access in the p2m (and with altp2m this should be the active one). But when is this check normally expected to fail? Tamas
_______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
