[PATCH V2] arm64: mm: Optimise tlb flush logic where we have >4K granule

[Steve Capper]

On Fri, May 02, 2014 at 01:59:06PM +0100, Will Deacon wrote:
> On Fri, May 02, 2014 at 01:31:28PM +0100, Steve Capper wrote:
> > On Fri, May 02, 2014 at 12:26:18PM +0100, Will Deacon wrote:
> > > On Fri, May 02, 2014 at 11:37:14AM +0100, Steve Capper wrote:
> > > > The tlb maintainence functions: __cpu_flush_user_tlb_range and
> > > > __cpu_flush_kern_tlb_range do not take into consideration the page
> > > > granule when looping through the address range, and repeatedly flush
> > > > tlb entries for the same page when operating with 64K pages.
> > > > 
> > > > This patch re-works the logic s.t. we instead advance the loop by
> > > >  1 << (PAGE_SHIFT - 12), so avoid repeating ourselves.
> > > > 
> > > > Also the routines have been converted from assembler to static inline
> > > > functions to aid with legibility and potential compiler optimisations.
> > > > 
> > > > Signed-off-by: Steve Capper <steve.capper at linaro.org>
> > > > Acked-by: Will Deacon <will.deacon at arm.com>
> > > > ---
> > > > Changed in V2: added the missing isb(.) to the kernel tlb flush.
> > > 
> > > Hold your horses ;)
> > 
> > :-)
> > 
> > > 
> > > You mentioned remapping kernel text rw/ro, but if you think about it, it's
> > > still executable for both of these, so the isb() isn't needed. Do we have a
> > > case for changing whether or not something is executable?
> > 
> > I think module loading and unloading in future would likely need this.
> > i.e. if we get stuff like set_memory_nx and friends for ARM64.
> > 
> > We've just had this added to ARM:
> >  75374ad ARM: mm: Define set_memory_* functions for ARM
> 
> Ok, but if it's just set_memory_nx that needs this, I'd rather put the isb()
> there instead of penalising all kernel TLB flushes.

Sure that makes sense, I can't think of any other scenarios that would
require this isb(.). I will document the fact that the isb has been
removed in the commit log for V3. Also...

Laura,
I'll add you to CC for the patch, as you're working on the set_memory_*
functions for ARM64.

Cheers,
-- 
Steve

> 
> Will