Re: [Xen-devel] [PATCH 3/8] xen/arm: Implement p2m_type_t as an enum

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-12-05 at 17:07 +0100, Tim Deegan wrote:
> At 15:52 +0000 on 05 Dec (1386255150), Ian Campbell wrote:
> > On Thu, 2013-12-05 at 15:42 +0000, Julien Grall wrote:
> > > Until now, Xen doesn't know the type of the page (ram, foreign page, 
> > > mmio,...).
> > > Introduce p2m_type_t with basic types:
> > >     - p2m_invalid: Nothing is mapped here
> > 
> > Do we really need this? Is it not equivalent to not setting the present
> > bit? I see x86 has the same type though -- Tim can you explain why.
> 
> There are other not-present types on x86: PoD, paged-out, emulated-MMIO.  

This means not Present doesn't imply invalid, I see. Even if we don't
currently have such types I can see how this makes sense. In theory when
we get short of bits we could consider the P bit one of the type bits,
which would give us 16 present and 16 not-present types. Overkill for
now I expect.

Is it ever the case that an actual p2m entry contains the p2m_invalid
bit pattern or is it more of a pseudo-type which is used internally and
as an API token in the hypervisor?

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel