Subject: [PATCH 06/10] arm64: tlbflush: avoid flushing when fullmm == 1

From: [email-masked] (Catalin Marinas)
Date: Mon, 5 Oct 2015 18:18:43 +0100

On Mon, Oct 05, 2015 at 05:33:13PM +0100, Will Deacon wrote:
> On Tue, Sep 29, 2015 at 10:29:58AM +0100, Catalin Marinas wrote:
> > On Thu, Sep 17, 2015 at 01:50:15PM +0100, Will Deacon wrote:
> > > The TLB gather code sets fullmm=1 when tearing down the entire address
> > > space for an mm_struct on exit or execve. Given that the ASID allocator
> > > will never re-allocate a dirty ASID, this flushing is not needed and can
> > > simply be avoided in the flushing code.
> > > 
> > > Signed-off-by: Will Deacon <[email-masked]>
> > > ---
> > >  arch/arm64/include/asm/tlb.h | 26 +++++++++++++++-----------
> > >  1 file changed, 15 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> > > index d6e6b6660380..ffdaea7954bb 100644
> > > --- a/arch/arm64/include/asm/tlb.h
> > > +++ b/arch/arm64/include/asm/tlb.h
> > > @@ -37,17 +37,21 @@ static inline void __tlb_remove_table(void *_table)
> > >  
> > >  static inline void tlb_flush(struct mmu_gather *tlb)
> > >  {
> > > -	if (tlb->fullmm) {
> > > -		flush_tlb_mm(tlb->mm);
> > > -	} else {
> > > -		struct vm_area_struct vma = { .vm_mm = tlb->mm, };
> > > -		/*
> > > -		 * The intermediate page table levels are already handled by
> > > -		 * the __(pte|pmd|pud)_free_tlb() functions, so last level
> > > -		 * TLBI is sufficient here.
> > > -		 */
> > > -		__flush_tlb_range(&vma, tlb->start, tlb->end, true);
> > > -	}
> > > +	struct vm_area_struct vma = { .vm_mm = tlb->mm, };
> > > +
> > > +	/*
> > > +	 * The ASID allocator will either invalidate the ASID or mark
> > > +	 * it as used.
> > > +	 */
> > > +	if (tlb->fullmm)
> > > +		return;
> > 
> > BTW, do we actually need this flush_tlb_mm() with the current ASID
> > allocator? It doesn't reuse old ASIDs either before a full TLBI (just
> > trying to remember if we had any logic; or maybe it was needed before
> > non-lazy __pte_free_tlb).
> 
> I'm afraid I don't follow you here. This diff is removing the flush_tlb_mm
> because, as you point out, it's no longer needed.

I don't think you are missing anything, just wondering why we had it
before (probably forgot to remove it when the non-lazy __pte_free_tlb
was added).

-- 
Catalin