Re: [patch 06/26] Xen-paravirt_ops: paravirt_ops: allocate a fixmap slot

Jeremy Fitzhardinge
2007-02-28T00:50:11Z

Jeremy Fitzhardinge wrote:
> Ingo Molnar wrote:
>
>> why not vmalloc it on the guest side? fixmaps are bad for this purpose
>> for a general paravirt implementation, it limits the size of the shared
>> info page, etc.
>>
>
> Yes. vmalloc would have the annoying side-effect of actually allocating
> some pages which would be shadowed by the remapping, but I guess
> get_vm_area would do the job. I'll give it a go.

Hm, this is a bit awkward. We need to map the shared info page fairly
early - say, around paging_init - but we're still on the bootmem
allocator at that point, so get_vm_area isn't usable yet. Using a
fixmap keeps things simple. It seems to me that having a single fixmap
available is useful for this kind of simple/early mapping, and if
someone needs to map something larger, then they can put it off until
get_vm_area() is available...

J