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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.07.13 at 16:01, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> On 12/07/2013 14:41, "Jan Beulich" <JBeulich@xxxxxxxx> 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?

Well, okay, I'll do it that way then. Are you okay with skipping the
locking during boot, just as done in __set_fixmap() in the current
version of the patch?

Jan


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