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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Oct 02, 2015 at 01:31:37AM -0600, Jan Beulich wrote:
> >>> 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.
> 

I think George and you are talking about another function?  Is there
anything that prevents this patch from being committed as-is?

Wei.

> Jan
> 
> 

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