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

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

On 2014/9/19 15:10, Jan Beulich wrote:
>>>> On 19.09.14 at 08:50, <tiejun.chen@intel.com> wrote:
>> On 2014/9/19 14:26, Jan Beulich wrote:
>>>>>> On 19.09.14 at 03:20, <tiejun.chen@intel.com> 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
>
>
>