Re: [Xen-devel] [v6][PATCH 2/2] xen:vtd: missing RMRR mapping while share EPT

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/9/19 15:10, Jan Beulich wrote:
> > > > On 19.09.14 at 08:50, <tiejun.chen@xxxxxxxxx> wrote:
> > On 2014/9/19 14:26, Jan Beulich wrote:
> > > > > > On 19.09.14 at 03:20, <tiejun.chen@xxxxxxxxx> wrote:
> > > > (XEN) [VT-D]dmar.c:807: found ACPI_DMAR_RMRR:
> > > > (XEN) [VT-D]dmar.c:383:  endpoint: 0000:00:14.0
> > > > (XEN) [VT-D]dmar.c:676:   RMRR region: base_addr ab805000 end_address
> > > > ab818fff
> > > > (XEN) [VT-D]dmar.c:807: found ACPI_DMAR_RMRR:
> > > > (XEN) [VT-D]dmar.c:383:  endpoint: 0000:00:02.0
> > > > (XEN) [VT-D]dmar.c:676:   RMRR region: base_addr ad000000 end_address
> > > > af7fffff
> > > So how does passing through either of these work for a guest with
> > > 4Gb or more of memory assigned with just the original 2 patches
> > > (and with shared page tables)? There ought to be a collision detected
> > > when trying to do the identity mapping.
> > Do you mean this point, mfn_valid(mfn)? If yes, I remember we made
> > agreement previously about how to cover three cases including this scenario:
> >
> > "
> > #1: !mfn_valid(mfn)
> >
> > We can create those mapping safely.
> >
> > #2: mfn_x(mfn) == gfn && p2mt == p2m_mmio_direct && a == p2m_access_rw
> >
> > We already have these matched mappings.
> >
> > #3: Others
> >
> > Return with that waring message: "Cannot identity map d%d:%lx, already
> > mapped to %lx but mismatch.\n"
> > "
> > And this is just as we did in patch #1:
> >
> > +
> > +    if ( !mfn_valid(mfn) )
> > +        ret = p2m_set_entry(p2m, gfn, _mfn(gfn), PAGE_ORDER_4K,
> > p2m_mmio_direct,
> > +                            p2m_access_rw);
> > +    else if ( mfn_x(mfn) == gfn &&
> > +              p2mt == p2m_mmio_direct &&
> > +              a == p2m_access_rw )
> > +        ret = 0;
> > +    else
> > +        printk(XENLOG_G_WARNING
> > +               "Cannot identity map d%d:%lx, already mapped to %lx.\n",
> > +               d->domain_id, gfn, mfn_x(mfn));
> Right, but the important point is that when the warning gets printed
> -EBUSY gets returned, i.e. in the end the device assignment is to fail.
> Are you seeing the warning when creating a large enough guest? If
My platform just own 4G memory, so after I try to set 'memory=15360' in 
domu.cfg, I can't boot such a VM:
# xl cr domu.cfg
Parsing config from domu.cfg
libxl: error: libxl.c:4202:libxl_set_memory_target: new target 0 for 
dom0 is below the minimum threshhold
...
failed to free memory for the domain

> not - can you explain why you don't see it (as I can't)?
Do you know exactly how to test this case as you expect here? Then I can 
take a further look to step on your question. Or I guess you are hinting 
something wrong should be happened but I never realize that previously.
Thanks
Tiejun

> Jan
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