linux-kernel - Re: [RFC PATCH 2/2] mm: mmu_notifier fix for tlb_end

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Date:   Fri, 24 Aug 2018 14:50:48 +0100
From:   Will Deacon <will.deacon@....com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        torvalds@...ux-foundation.org, luto@...nel.org, x86@...nel.org,
        bp@...en8.de, riel@...riel.com, jannh@...gle.com,
        ascannell@...gle.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        David Miller <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-arch@...r.kernel.org, Palmer Dabbelt <palmer@...ive.com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [RFC PATCH 2/2] mm: mmu_notifier fix for tlb_end_vma (build
 failures)

On Fri, Aug 24, 2018 at 02:34:27PM +0100, Will Deacon wrote:
> On Fri, Aug 24, 2018 at 06:24:19AM -0700, Guenter Roeck wrote:
> > On Fri, Aug 24, 2018 at 02:10:27PM +0100, Will Deacon wrote:
> > > On Fri, Aug 24, 2018 at 06:07:22AM -0700, Guenter Roeck wrote:
> > > > On Thu, Aug 23, 2018 at 06:47:09PM +1000, Nicholas Piggin wrote:
> > > > > The generic tlb_end_vma does not call invalidate_range mmu notifier,
> > > > > and it resets resets the mmu_gather range, which means the notifier
> > > > > won't be called on part of the range in case of an unmap that spans
> > > > > multiple vmas.
> > > > > 
> > > > > ARM64 seems to be the only arch I could see that has notifiers and
> > > > > uses the generic tlb_end_vma. I have not actually tested it.
> > > > > 
> > > > > Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> > > > > Acked-by: Will Deacon <will.deacon@....com>
> > > > 
> > > > This patch breaks riscv builds in mainline.
> > > 
> > > Looks very similar to the breakage we hit on arm64. diff below should fix
> > > it.
> > > 
> > 
> > Unfortunately it doesn't.
> > 
> > In file included from ./arch/riscv/include/asm/pgtable.h:26:0,
> >                  from ./include/linux/memremap.h:7,
> >                  from ./include/linux/mm.h:27,
> >                  from arch/riscv/mm/fault.c:23:
> > ./arch/riscv/include/asm/tlb.h: In function ‘tlb_flush’:
> > ./arch/riscv/include/asm/tlb.h:19:18: error: dereferencing pointer to incomplete type ‘struct mmu_gather’
> >   flush_tlb_mm(tlb->mm);
> >                   ^
> 
> Sorry, I was a bit quick of the mark there. You'll need a forward
> declaration for the paramater type. Here it is with a commit message,
> although still untested because I haven't got round to setting up a riscv
> toolchain yet.
> 
> Will
> 
> --->8
> 
> From adb9be33d68320edcda80d540a97a647792894d2 Mon Sep 17 00:00:00 2001
> From: Will Deacon <will.deacon@....com>
> Date: Fri, 24 Aug 2018 14:33:48 +0100
> Subject: [PATCH] riscv: tlb: Provide definition of tlb_flush() before
>  including tlb.h
> 
> As of commit fd1102f0aade ("mm: mmu_notifier fix for tlb_end_vma"),
> asm-generic/tlb.h now calls tlb_flush() from a static inline function,
> so we need to make sure that it's declared before #including the
> asm-generic header in the arch header.
> 
> Since tlb_flush() is a one-liner for riscv, we can define it before
> including asm-generic/tlb.h as long as we provide a forward declaration
> of struct mmu_gather.
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  arch/riscv/include/asm/tlb.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/tlb.h b/arch/riscv/include/asm/tlb.h
> index c229509288ea..a3d1380ad970 100644
> --- a/arch/riscv/include/asm/tlb.h
> +++ b/arch/riscv/include/asm/tlb.h
> @@ -14,11 +14,13 @@
>  #ifndef _ASM_RISCV_TLB_H
>  #define _ASM_RISCV_TLB_H
>  
> -#include <asm-generic/tlb.h>
> +struct mmu_gather;
>  
>  static inline void tlb_flush(struct mmu_gather *tlb)
>  {
>  	flush_tlb_mm(tlb->mm);

Bah, didn't spot the dereference so this won't work either. You basically
just need to copy what I did for arm64 in d475fac95779.

Will