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

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Date:   Fri, 24 Aug 2018 14:34:27 +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 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);
 }
 
+#include <asm-generic/tlb.h>
+
 #endif /* _ASM_RISCV_TLB_H */
-- 
2.7.4