linux-kernel - Re: [PATCH 12/18] arch/tlb: Clean up simple architectures

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Message-ID: <C2D7FE5348E1B147BCA15975FBA23075012B09A59E@us01wembx1.internal.synopsys.com>
Date:   Wed, 3 Oct 2018 17:03:50 +0000
From:   Vineet Gupta <vineet.gupta1@...opsys.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "npiggin@...il.com" <npiggin@...il.com>
CC:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
        "riel@...riel.com" <riel@...riel.com>,
        "Richard Henderson" <rth@...ddle.net>,
        Vineet Gupta <vineet.gupta1@...opsys.com>,
        "Mark Salter" <msalter@...hat.com>,
        Richard Kuo <rkuo@...eaurora.org>,
        Michal Simek <monstr@...str.eu>,
        Paul Burton <paul.burton@...s.com>,
        Greentime Hu <green.hu@...il.com>,
        Ley Foon Tan <lftan@...era.com>,
        Jonas Bonn <jonas@...thpole.se>, Helge Deller <deller@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Guan Xuetao <gxt@....edu.cn>, Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH 12/18] arch/tlb: Clean up simple architectures

On 09/26/2018 04:56 AM, Peter Zijlstra wrote:
> There are generally two cases:
>
>  1) either the platform has an efficient flush_tlb_range() and
>     asm-generic/tlb.h doesn't need any overrides at all.
>
>  2) or an architecture lacks an efficient flush_tlb_range() and
>     we override tlb_end_vma() and tlb_flush().
>
> Convert all 'simple' architectures to one of these two forms.
>
> alpha:	    has no range invalidate -> 2
> arc:	    already used flush_tlb_range() -> 1
> c6x:	    has no range invalidate -> 2
> h8300:	    has no mmu
> hexagon:    has an efficient flush_tlb_range() -> 1
>             (flush_tlb_mm() is in fact a full range invalidate,
> 	     so no need to shoot down everything)
> m68k:	    has inefficient flush_tlb_range() -> 2
> microblaze: has no flush_tlb_range() -> 2
> mips:	    has efficient flush_tlb_range() -> 1
> 	    (even though it currently seems to use flush_tlb_mm())
> nds32:	    already uses flush_tlb_range() -> 1
> nios2:	    has inefficient flush_tlb_range() -> 2
> 	    (no limit on range iteration)
> openrisc:   has inefficient flush_tlb_range() -> 2
> 	    (no limit on range iteration)
> parisc:	    already uses flush_tlb_range() -> 1
> sparc32:    already uses flush_tlb_range() -> 1
> unicore32:  has inefficient flush_tlb_range() -> 2
> 	    (no limit on range iteration)
> xtensa:	    has efficient flush_tlb_range() -> 1
>
> Cc: Richard Henderson <rth@...ddle.net>
> Cc: Vineet Gupta <vgupta@...opsys.com>
> Cc: Mark Salter <msalter@...hat.com>
> Cc: Richard Kuo <rkuo@...eaurora.org>
> Cc: Michal Simek <monstr@...str.eu>
> Cc: Paul Burton <paul.burton@...s.com>
> Cc: Greentime Hu <green.hu@...il.com>
> Cc: Ley Foon Tan <lftan@...era.com>
> Cc: Jonas Bonn <jonas@...thpole.se>
> Cc: Helge Deller <deller@....de>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Guan Xuetao <gxt@....edu.cn>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Nick Piggin <npiggin@...il.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/alpha/include/asm/tlb.h      |    2 --
>  arch/arc/include/asm/tlb.h        |   23 -----------------------
>  arch/c6x/include/asm/tlb.h        |    1 +
>  arch/h8300/include/asm/tlb.h      |    2 --
>  arch/hexagon/include/asm/tlb.h    |   12 ------------
>  arch/m68k/include/asm/tlb.h       |    1 -
>  arch/microblaze/include/asm/tlb.h |    4 +---
>  arch/mips/include/asm/tlb.h       |    8 --------
>  arch/nds32/include/asm/tlb.h      |   10 ----------
>  arch/nios2/include/asm/tlb.h      |    8 +++++---
>  arch/openrisc/include/asm/tlb.h   |    6 ++++--
>  arch/parisc/include/asm/tlb.h     |   13 -------------
>  arch/powerpc/include/asm/tlb.h    |    1 -
>  arch/sparc/include/asm/tlb_32.h   |   13 -------------
>  arch/unicore32/include/asm/tlb.h  |   10 ++++++----
>  arch/xtensa/include/asm/tlb.h     |   17 -----------------
>  16 files changed, 17 insertions(+), 114 deletions(-)
>
> --- a/arch/alpha/include/asm/tlb.h
> +++ b/arch/alpha/include/asm/tlb.h
> @@ -4,8 +4,6 @@
>  
>  #define tlb_start_vma(tlb, vma)			do { } while (0)
>  #define tlb_end_vma(tlb, vma)			do { } while (0)
> -#define __tlb_remove_tlb_entry(tlb, pte, addr)	do { } while (0)
> -
>  #define tlb_flush(tlb)				flush_tlb_mm((tlb)->mm)
>  
>  #include <asm-generic/tlb.h>
> --- a/arch/arc/include/asm/tlb.h
> +++ b/arch/arc/include/asm/tlb.h
> @@ -9,29 +9,6 @@
>  #ifndef _ASM_ARC_TLB_H
>  #define _ASM_ARC_TLB_H
>  
> -#define tlb_flush(tlb)				\
> -do {						\
> -	if (tlb->fullmm)			\
> -		flush_tlb_mm((tlb)->mm);	\
> -} while (0)
> -
> -/*
> - * This pair is called at time of munmap/exit to flush cache and TLB entries
> - * for mappings being torn down.
> - * 1) cache-flush part -implemented via tlb_start_vma( ) for VIPT aliasing D$
> - * 2) tlb-flush part - implemted via tlb_end_vma( ) flushes the TLB range
> - *
> - * Note, read https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.org_lkml_2004_1_15_6&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=c14YS-cH-kdhTOW89KozFhBtBJgs1zXscZojEZQ0THs&m=5jiyvgRek4SKK5DUWDBGufVcuLez5G-jJCh3K-ndHsg&s=7uAzzw_jdAXMfb07B-vGPh3V1vggbTAsB7xL6Kie47A&e=
> - */
> -
> -#define tlb_end_vma(tlb, vma)						\
> -do {									\
> -	if (!tlb->fullmm)						\
> -		flush_tlb_range(vma, vma->vm_start, vma->vm_end);	\
> -} while (0)
> -
> -#define __tlb_remove_tlb_entry(tlb, ptep, address)
> -
>  #include <linux/pagemap.h>
>  #include <asm-generic/tlb.h>

LGTM per discussion in an earlier thread. However given that for "simpler" arches
the whole series doesn't apply can you please beef up the changelog so I don't go
scratching my head 2 years down the line. It currently describes the hows of
things but not exactly whys: shift_arg_pages missing tlb_start_vma,
move_page_tables look dodgy, yady yadda ?

Thx,
-Vineet