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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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
not - can you explain why you don't see it (as I can't)?

Jan


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