> On Oct 18, 2018, at 9:26 AM, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > >> On 2018-10-12 11:02:18 [-0700], Andy Lutomirski wrote: >> On Fri, Oct 12, 2018 at 10:54 AM Dave Hansen >> <dave.hansen@xxxxxxxxxxxxxxx> wrote: >>> >>>> On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote: >>>> The PKRU value is not set for kernel threads because they do not have >>>> the ->initialized value set. As a result the kernel thread has a random >>>> PKRU value set which it inherits from the previous task. >>>> It has been suggested by Paolo Bonzini to set it for kernel threads, too >>>> because it might be a fix. >>>> I *think* this is not required because the kernel threads don't copy >>>> data to/from userland and don't have access to any userspace mm in >>>> general. >>>> However there is this use_mm(). If we gain a mm by use_mm() we don't >>>> have a matching PKRU value because those are per thread. It has been >>>> suggested to use 0 as the PKRU value but this would bypass PKRU. >>>> >>>> Set the initial (default) PKRU value for kernel threads. >>> >>> We might want to do this for cleanliness reasons... Maybe. >>> >>> But this *should* have no practical effects. Kernel threads have no >>> real 'mm' and no user pages. They should not have do access to user >>> mappings. Protection keys *only* apply to user mappings. Thus, >>> logically, they should never be affected by PKRU values. >>> >>> So I'm kinda missing the point of the patch. >> >> use_mm(). > > So. I would drop that patch from queue. Anyone feels different about it? > I think we *do* want the patch. It’s a bugfix for use_mm users, right? > Sebastian
