Re: [v3][PATCH 03/16] xen/vtd: create RMRR mapping

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

On 2015/6/11 22:07, Tim Deegan wrote:
> At 17:31 +0800 on 11 Jun (1434043916), Chen, Tiejun wrote:
>>>>        while ( base_pfn < end_pfn )
>>>>        {
>>>> -        int err = intel_iommu_map_page(d, base_pfn, base_pfn,
>>>> -                                       IOMMUF_readable|IOMMUF_writable);
>>>> +        int err = set_identity_p2m_entry(d, base_pfn, p2m_access_rw);
>>>>
>>>>            if ( err )
>>>>                return err;
>>>
>>> Tim has another comment to replace earlier unmap with
>>
>> Yes, I knew this.
>>
>>> guest_physmap_remove_page() which will call iommu
>>> unmap internally. Please include this change too.
>>>
>>
>> But,
>>
>> guest_physmap_remove_page()
>>       |
>>       + p2m_remove_page()
>> 	|
>> 	+ iommu_unmap_page()
>> 	|
>> 	+ p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), xxx)
>>
>> I think this already remove these pages both on ept/vt-d sides, right?
>
> Yes; this is about this code further up in the same function:
>
>             while ( base_pfn < end_pfn )
>             {
>                 if ( intel_iommu_unmap_page(d, base_pfn) )
>                     ret = -ENXIO;
>                 base_pfn++;
>             }
>
> which ought to be calling guest_physmap_remove_page() or similar, to
> make sure that both iommu and EPT mappings get removed.
>

I still just think current implementation might be fine at this point.

We have two scenarios here, the case of shared ept and the case of 
non-shared ept. But no matter what case we're tracking, shouldn't 
guest_physmap_remove_page() always call p2m->set_entry() to clear *all* 
*valid* mfn which is owned by a given VM? And p2m->set_entry() also 
calls iommu_unmap_page() internally. So nothing special should further 
consider.

If I'm wrong or misunderstanding, please correct me :)

Thanks
Tiejun