Re: [Xen-devel] [PATCH v2] x86/p2m-pt: tighten conditions of IOMMU mapping updates

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> George Dunlap <george.dunlap@xxxxxxxxxx> 10/01/15 6:16 PM >>>
>On 01/10/15 11:25, Jan Beulich wrote:
>> TBD: As already mentioned on the large-page-MMIO-mapping patch, there
>>      is an apparent inconsistency with PoD handling: 2M mappings get
>>      valid entries created, while 4k mappings don't. It would seem to
>>      me that the 4k case needs changing, even if today this may only
>>      be a latent bug. Question of course is why we don't rely on
>>      p2m_type_to_flags() doing its job properly and instead special
>>      case certain P2M types.
>
>The inconsistency in the conditionals there is a bit strange; but I'm
>pretty sure that in the 2MB case it is (at the moment) superfluous,
>because at the moment it seems that when setting a page with type
>p2m_populate_on_demand, it's always passing in _mfn(0), which is valid.
>
>(It used to pass a magic MFN, but Tim Deegan switched it to _mfn(0) at
>some point without comment.)

Perhaps just because the magic MFN didn't always work? Tim?
To me it looks wrong to pass anything other than INVALID_MFN
there.

Jan




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