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

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Message-ID: <mhng-86a3cd0c-c3dc-42a9-a955-01fbce9d2797@palmer-si-x1c4>
Date:   Fri, 24 Aug 2018 16:32:12 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Will Deacon <will.deacon@....com>
CC:     linux@...ck-us.net, npiggin@...il.com, peterz@...radead.org,
        Linus Torvalds <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,
        davem@...emloft.net, schwidefsky@...ibm.com, mpe@...erman.id.au,
        linux-arch@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject:     Re: [RFC PATCH 2/2] mm: mmu_notifier fix for tlb_end_vma (build failures)

On Fri, 24 Aug 2018 06:50:48 PDT (-0700), Will Deacon wrote:
> 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.

FWIW, Arnd built them last time he updated the cross tools so you should be 
able to get GCC 8.1.0 for RISC-V from there.  I use this make.cross script that 
I stole from the Intel 0-day robot

    https://github.com/palmer-dabbelt/home/blob/master/.local/src/local-scripts/make.cross.bash

If I'm reading it correctly the tools come from here

    http://cdn.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/x86_64-gcc-8.1.0-nolibc-riscv64-linux.tar.gz

I use the make.cross script as it makes it super easy to test my 
across-the-tree patches on other people's ports.

>>
>> 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