Re: [PATCH v2] add locking around certain calls to map_pages_to_xen()

[Keir Fraser <keir.xen@gmail.com>]

On 12/07/2013 14:41, "Jan Beulich" <JBeulich@suse.com> wrote:

>> Is it unsafe to just stick a lock around the guts of map_pages_to_xen(), or
>> at least the parts that add new page tables?
> 
> I'm not certain about the safety of this, but clearly two CPUs
> changing entirely different parts of the address space don't need
> to lock out one another, so I rather view adding a global lock here
> as being (potentially) harmful in terms of performance (and hence
> the thought of locking at page table entry granularity instead).

Ah, I see. Well, locking only on changes to page-directory entries wouldn't
be too bad, even if it were a single global lock? That would be a rare
occurrence. It's reasonable to assume that callers will not conflict on the
page-aligned regions they modify, so this would suffice?

 -- Keir