Re: MIPS: Make set_pte() SMP safe.

[Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>]

David,

On 08/04/2015 01:48 PM, David Daney wrote:
> I think the best way to think about it is to ignore vmap, and consider 
> the semantics of set_pte().
> ...
> You can go around in circles all you want trying to indirectly avoid 
> using the buddy-PTE from another thread, but I think it is best to 
> make set_pte() have easily understood semantics (and semantics that 
> match those of other architectures) and not clobber things in 
> unexpected ways.

My primary interest here is not a semantics of set_pte() but the 
followup of your finding, I tried test it: if guard page logic doesn't 
work anymore (as I can judge basing on your observations) then it calls 
back my old optimization in flush_cache_vmap(start, end) and similar. 
Right now it flushes the whole cache because if it tries to flush a 
guard page (and it THERE IS such attempt in some mm/*.c) it does TLB 
exception and I have a hard lock in do_page_fault().

Issue is significant for some GPU/display drivers which calls flushing 
VMALLOC area pretty often.