Re: [RFC PATCH 2/4] iommu/vt-d: Add first level page table interfaces

[Lu Baolu]

Hi Kevin,

On 9/25/19 3:32 PM, Tian, Kevin wrote:
> > From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx]
> > Sent: Wednesday, September 25, 2019 2:52 PM
> >
> > Hi Peter and Kevin,
> >
> > On 9/25/19 1:24 PM, Peter Xu wrote:
> > > On Wed, Sep 25, 2019 at 04:38:31AM +0000, Tian, Kevin wrote:
> > > > > From: Peter Xu [mailto:peterx@xxxxxxxxxx]
> > > > > Sent: Wednesday, September 25, 2019 12:31 PM
> > > > >
> > > > > On Tue, Sep 24, 2019 at 09:38:53AM +0800, Lu Baolu wrote:
> > > > > > > > intel_mmmap_range(domain, addr, end, phys_addr, prot)
> > > > > > >
> > > > > > > Maybe think of a different name..? mmmap seems a bit weird :-)
> > > > > >
> > > > > > Yes. I don't like it either. I've thought about it and haven't
> > > > > > figured out a satisfied one. Do you have any suggestions?
> > > > >
> > > > > How about at least split the word using "_"?  Like "mm_map", then
> > > > > apply it to all the "mmm*" prefixes.  Otherwise it'll be easily
> > > > > misread as mmap() which is totally irrelevant to this...
> > > >
> > > > what is the point of keeping 'mm' here? replace it with 'iommu'?
> > >
> > > I'm not sure of what Baolu thought, but to me "mm" makes sense itself
> > > to identify this from real IOMMU page tables (because IIUC these will
> > > be MMU page tables).  We can come up with better names, but IMHO
> > > "iommu" can be a bit misleading to let people refer to the 2nd level
> > > page table.
> >
> > "mm" represents a CPU (first level) page table;
> >
> > vs.
> >
> > "io" represents an IOMMU (second level) page table.
>
> IOMMU first level is not equivalent to CPU page table, though you can
> use the latter as the first level (e.g. in SVA). Especially here you are
> making IOVA->GPA as the first level, which is not CPU page table.
>
> btw both levels are for "io" i.e. DMA purposes from VT-d p.o.v. They
> are just hierarchical structures implemented by VT-d, with slightly
> different format. The specification doesn't limit how you use them for.
> In a hypothetical case, an IOMMU may implement exactly same CPU-page-
> table format and support page faults for both levels. Then you can even
> link the CPU page table to the 2nd level for sure.

Fair enough. A good conceptual gap fix.

> Maybe we just name it from VT-d context, e.g. intel_map_first_level_range,
> Intel_map_second_level_range, and then register them as dmar domain
> callback as you replied in another mail.

Yes. Make sense.

> Thanks
> Kevin

Best regards,
Baolu