Re: [Xen-devel] [V9 PATCH 7/8] pvh dom0: check for vioapic null ptr in vioapic_range

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Wed, 23 Apr 2014 10:07:25 +0100
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 23.04.14 at 02:11, <mukesh.rathor@xxxxxxxxxx> wrote:
> > On Tue, 22 Apr 2014 08:33:29 +0100
> > "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> >> >>> On 22.04.14 at 02:59, <mukesh.rathor@xxxxxxxxxx> wrote:
......

> >   So it must have been the third one that I had observed the
> >   vioapic_range crash in a while ago, and had made note of it.
> > Looking at it:
> > 
> >     if ( (p2mt == p2m_mmio_dm) ||
> >          (access_w && (p2mt == p2m_ram_ro)) )
> >     {
> >         put_gfn(p2m->domain, gfn);
> >         if ( !handle_mmio() )
> > 
> > doesn't seem apply to domu. Unfortunately, I can't reproduce it now
> > so maybe it was an ept violation due to some bug, and a crash in 
> > vioapic_range before printing the gfn/mfns etc by
> > ept_handle_violation made me make a note to put a check in it.
> 
> Which makes me think that we don't need the patch at all.

Well, without this patch, in case of dom0 EPT violation, dom0 will
not die gracefully printing gfn/mfn/etc.. info. But instead it will
show fault in vioapic_range. 


ept_handle_violation() 
       hvm_hap_nested_page_fault()
             -> handle_mmio() -----> vioapic_range() : KABOOM!!

       gdprintk(XENLOG_ERR, "EPT violation %#lx (%c%c%c/%c%c%c), "
                    "gpa %#"PRIpaddr", mfn %#lx, type %i.\n",
                                 qualification,  <=== NOT REACHED
          .......

I can submit it later too I guess. But without it, we'd not know
the ept violation crashes.

thanks
mukesh


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