Re: [Xen-devel] [PATCH 1/1] xen:vtd: missing RMRR mapping while share EPT

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.07.14 at 11:56, <tiejun.chen@xxxxxxxxx> wrote:
> On 2014/7/24 17:41, Jan Beulich wrote:
>>>>> On 24.07.14 at 10:28, <tiejun.chen@xxxxxxxxx> wrote:
>>> On 2014/7/24 15:45, Jan Beulich wrote:
>>>>>>> On 24.07.14 at 09:00, <tiejun.chen@xxxxxxxxx> wrote:
>>>>> On 2014/7/24 14:14, Jan Beulich wrote:
>>>>>>>>> On 24.07.14 at 03:23, <tiejun.chen@xxxxxxxxx> wrote:
>>>>>>> @@ -1867,7 +1869,21 @@ static int rmrr_identity_mapping(struct domain 
>>>>>>> *d,
>>>>>>>
>>>>>>>          while ( base_pfn < end_pfn )
>>>>>>>          {
>>>>>>> -        if ( intel_iommu_map_page(d, base_pfn, base_pfn,
>>>>>>> +        if ( iommu_use_hap_pt(d) )
>>>>>>
>>>>>> Don't you, btw, need to extend this condition by
>>>>>> && (!iommu_passthrough || !is_hardware_domain(d))?
>>>>>
>>>>> Why do we need these checks here?
>>>>
>>>> At least for documentation purposes: It would be wrong to try to
>>>> establish these mappings. I reckon iommu_use_hap_pt() implies the
>>>> combined other condition, so an ASSERT() would presumably be fine
>>>> as well (and get even closer to the intended documentation purpose).
>>>>
>>>
>>> I think if() should be reasonable here. Because
>>>
>>> intel_iommu_map_page()
>>> {
>>>     ...
>>>       /* do nothing if dom0 and iommu supports pass thru */
>>>       if ( iommu_passthrough && is_hardware_domain(d) )
>>>           return 0;
>>>
>>> We just do nothing to return simply. But if ASSERT will cause abort.
>>
>> Then tell me the scenario where iommu_use_hap_pt(d) is true and
>> both iommu_passthrough and is_hardware_domain(d) are true too.
> 
> Then HVM?

If we will ever see a HVM Dom0 it'll clearly also require
!iommu_passthrough, just like PVH does - this mode is solely for PV.

> Anyway I did a test like this,
> 
>       if (iommu_use_hap_pt(d))
>       {
>               ASSERT (iommu_passthrough && is_hardware_domain(d));
> 
> Then Xen really reboot.

Of course, because you inverted the condition. You want

        ASSERT(!iommu_passthrough || !is_hardware_domain(d));

i.e. what I had previously suggested to add with && to the original
condition.

Jan


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