Re: [Xen-devel] Xen with dom0 pvops on ultra-recent "git tip"kernel on x86_64

[Christophe Saout <christophe@xxxxxxxx>]

Hi Keir,

> > There is some logic in the native Xen kernel which prevents a call to
> > mm_unpin if there are "foreign mappings", i.e. set by
> > direct_remap_pfn_range.  What's up with that?
> 
> It's subtle. Whether it is needed depends on whether the pv_ops kernel
> detects mappings of non-reference-counted memory by putting a flag in the
> relevant PTEs, or by the more subtle means used in our 2.6.18 kernel (see
> include/asm-i386/mach-xen/asm/maddr.h:mfn_to_local_pfn() and the comment
> above it). In the former case the flag would not be needed, and I think that
> is what Jeremy implemented.

Ok, I think I get it.  I do however not have the big picture, so I'm
trying the "try and fail and learn" approach right now.  There are some
subtle differences between the native and the pvops kernel regarding
definition of some pte macros/calls which are causing errors when I just
copy & paste some of the code over.  Let's see if I can get it to work.

There are some parts of the code doing early io remappings in the kernel
which are very helpful, also a bunch of checks in the necessary places
are already there which is definitely helpful.

> The flag would possibly still be needed for grant mappings in user space
> though (i.e., mappings made via the gntdev device driver, or by the blktap
> device driver).

I think this part has been deliberately left out, I'll leave that to
Jeremy. :-)

Thanks,
        Christophe



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