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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.09.14 at 03:20, <tiejun.chen@xxxxxxxxx> wrote:
> On 2014/9/18 17:09, Jan Beulich wrote:
>>>>> On 30.07.14 at 03:36, <tiejun.chen@xxxxxxxxx> wrote:
>>> --- a/xen/drivers/passthrough/vtd/iommu.c
>>> +++ b/xen/drivers/passthrough/vtd/iommu.c
>>> @@ -1867,8 +1867,14 @@ static int rmrr_identity_mapping(struct domain *d,
>>>
>>>       while ( base_pfn < end_pfn )
>>>       {
>>> -        if ( intel_iommu_map_page(d, base_pfn, base_pfn,
>>> -                                  IOMMUF_readable|IOMMUF_writable) )
>>> +        if ( iommu_use_hap_pt(d) )
>>> +        {
>>> +            ASSERT(!iommu_passthrough || !is_hardware_domain(d));
>>> +            if ( set_identity_p2m_entry(d, base_pfn) )
>>> +                return -1;
>>> +        }
>>> +        else if ( intel_iommu_map_page(d, base_pfn, base_pfn,
>>> +                                       IOMMUF_readable|IOMMUF_writable) )
>>>               return -1;
>>>           base_pfn++;
>>>       }
>>
>> So I gave this a try on the one box I have which exposes RMRRs
>> (since those are for USB devices I also used your patch to drop
>> the USB special casing as done in your later patch series, and I
>> further had to fiddle with vtd_ept_page_compatible() in order to
>> get page table sharing to actually work on that box [I'll send the
>> resulting patch later]) - with the result that passing through an
>> affected USB controller (as expected) doesn't work anymore. Which
> 
> With or without these two patches, USB always can be passed through in 
> my platform. Note I'm using ubuntu as a Guest OS.
> 
>> raises the question why the two patches alone would work at all.
>> Could you please share information on the address ranges specified
>> by the RMRR(s) in your case? I simply wonder whether things just
> 
> (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.

Jan


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