linux-kernel - Re: [tip:x86/mm] x86/mm/tlb: Leave lazy TLB mode at page table free time

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Date:   Wed, 25 Jul 2018 03:00:52 +0200
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, mingo@...nel.org, songliubraving@...com,
        torvalds@...ux-foundation.org, riel@...riel.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, dave.hansen@...el.com,
        linux-tip-commits@...r.kernel.org, rafael.tinoco@...aro.org
Subject: Re: [tip:x86/mm] x86/mm/tlb: Leave lazy TLB mode at page table free
 time

On 2018-07-17 13:46, Peter Zijlstra wrote:
> On Tue, Jul 17, 2018 at 02:34:07AM -0700, tip-bot for Rik van Riel wrote:
> > diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> > index 3063125197ad..e811ef7b8350 100644
> > --- a/include/asm-generic/tlb.h
> > +++ b/include/asm-generic/tlb.h
> > @@ -303,4 +303,14 @@ static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
> >  
> >  #define tlb_migrate_finish(mm) do {} while (0)
> >  
> > +/*
> > + * Used to flush the TLB when page tables are removed, when lazy
> > + * TLB mode may cause a CPU to retain intermediate translations
> > + * pointing to about-to-be-freed page table memory.
> > + */
> > +#ifndef HAVE_TLB_FLUSH_REMOVE_TABLES
> > +#define tlb_flush_remove_tables(mm) do {} while (0)
> > +#define tlb_flush_remove_tables_local(mm) do {} while (0)
> > +#endif
> 
> Is there a reason these are not inline functions, which gets us type
> checking and the like?

More to that, when building (linux-next tag: next-20180724) on arm 32
there is this build error when CONFIG_MMU is enabled, asm-generic/tlb.h
isn't included, see arch/arm/include/asm/tlb.h.

  CC      mm/memory.o
mm/memory.c: In function ‘tlb_remove_table_smp_sync’:
mm/memory.c:339:2: error: implicit declaration of function ‘tlb_flush_remove_tables_local’; did you mean ‘tlb_remove_table’? [-Werror=implicit-function-declaration]
  tlb_flush_remove_tables_local(mm);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  tlb_remove_table
mm/memory.c: In function ‘tlb_table_flush’:
mm/memory.c:372:2: error: implicit declaration of function ‘tlb_flush_remove_tables’; did you mean ‘tlb_remove_table’? [-Werror=implicit-function-declaration]
  tlb_flush_remove_tables(tlb->mm);
  ^~~~~~~~~~~~~~~~~~~~~~~
  tlb_remove_table

Alternative could be setting in every architecture's asm/tlb.h but that
doesn't make much sense. Other way would be to include prototype in
arch/arm/include/asm/tlb.h, not sure if that would be the best. Is
there any other place this could be defined for fixing issue in arm 32
bit ?

Cheers,
Anders