Re: [Xen-devel] [PATCH] xen/tmem: Don't use map_domain_page for long-life-time pages.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.06.13 at 15:55, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2013-06-13 at 14:49 +0100, Jan Beulich wrote:
>> >>> On 13.06.13 at 15:24, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>> > Did I understand correctly that the map_domain_page() was required on 
>> >  >5TiB systems, presumably because of limited virtual address space?  In 
>> > which case this code will fail on those systems?
>> > 
>> > If that is the case, then we need to have a way to make sure tmem cannot 
>> > be enabled on such systems.
>> 
>> Tmem is full of assumptions that all memory is mapped, and hence
>> one of the requirements here was to disable tmem when that
>> assumption is not true (until eventually tmem would get fixed).
> 
> Isn't this change moving it further away from that fixed state though?

In a way, yes. But what do you do? The code already assumes it
can use mfn_to_virt() or alike on memory taken from
alloc_domheap_pages(), so it's just being made consistently
wrong in doing it one more time. Any alternative fix would be way
more involved, as it would require adding the (un-)mapping around
the actual use points of the memory.

Jan


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