Date:   Tue, 17 Dec 2019 09:51:38 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Burton <paulburton@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Richard Henderson <rth@...ddle.net>,
        Nick Hu <nickhu@...estech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 05/17] asm-generic/tlb: Rename
 HAVE_RCU_TABLE_NO_INVALIDATE

On Mon, Dec 16, 2019 at 04:14:19PM +0100, Peter Zijlstra wrote:
> It seems to me you need something like this here patch, all you need to
> add is a suitable definition of tlb_needs_table_invalidate() for Power.

FWIW, Paul (Burton), MIPS should be able to have
tlb_needs_table_invalidate() return false when it has pure software TLB
fill. I tried to have a quick look for P5600 and P6600 to see if I could
find the right state that indicates hardware TLB, but couldn't find
anything.

> ---
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index c44ef15866a3..98de654b79b3 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -400,10 +400,6 @@ config MMU_GATHER_RCU_TABLE_FREE
>  	bool
>  	select MMU_GATHER_TABLE_FREE
>  
> -config MMU_GATHER_NO_TABLE_INVALIDATE
> -	bool
> -	depends on MMU_GATHER_RCU_TABLE_FREE
> -
>  config MMU_GATHER_PAGE_SIZE
>  	bool
>  
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 3dea4c8d39f2..2ddf24822d5b 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -223,7 +223,6 @@ config PPC
>  	select HAVE_PERF_REGS
>  	select HAVE_PERF_USER_STACK_DUMP
>  	select MMU_GATHER_RCU_TABLE_FREE		if SMP
> -	select MMU_GATHER_NO_TABLE_INVALIDATE	if MMU_GATHER_RCU_TABLE_FREE
>  	select MMU_GATHER_PAGE_SIZE
>  	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_RELIABLE_STACKTRACE		if PPC_BOOK3S_64 && CPU_LITTLE_ENDIAN
> diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
> index a76e915ab207..acf20b6c0a54 100644
> --- a/arch/sparc/Kconfig
> +++ b/arch/sparc/Kconfig
> @@ -66,7 +66,6 @@ config SPARC64
>  	select HAVE_KRETPROBES
>  	select HAVE_KPROBES
>  	select MMU_GATHER_RCU_TABLE_FREE if SMP
> -	select MMU_GATHER_NO_TABLE_INVALIDATE if MMU_GATHER_RCU_TABLE_FREE
>  	select HAVE_MEMBLOCK_NODE_MAP
>  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
>  	select HAVE_DYNAMIC_FTRACE
> diff --git a/arch/sparc/include/asm/tlb_64.h b/arch/sparc/include/asm/tlb_64.h
> index a2f3fa61ee36..ac8e74a96122 100644
> --- a/arch/sparc/include/asm/tlb_64.h
> +++ b/arch/sparc/include/asm/tlb_64.h
> @@ -28,6 +28,12 @@ void flush_tlb_pending(void);
>  #define __tlb_remove_tlb_entry(tlb, ptep, address) do { } while (0)
>  #define tlb_flush(tlb)	flush_tlb_pending()
>  
> +/*
> + * SPARC64's hardware TLB fill does not use the Linux page-tables
> + * and therefore we don't need a TLBI when freeing page-table pages.
> + */
> +#define tlb_needs_table_invalidate()	(false)
> +
>  #include <asm-generic/tlb.h>
>  
>  #endif /* _SPARC64_TLB_H */
> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> index fe0ea6ff3636..4108d6d18ca5 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -156,13 +156,6 @@
>   *  Useful if your architecture doesn't use IPIs for remote TLB invalidates
>   *  and therefore doesn't naturally serialize with software page-table walkers.
>   *
> - *  MMU_GATHER_NO_TABLE_INVALIDATE
> - *
> - *  This makes MMU_GATHER_RCU_TABLE_FREE avoid calling tlb_flush_mmu_tlbonly()
> - *  before freeing the page-table pages. This can be avoided if you use
> - *  MMU_GATHER_RCU_TABLE_FREE and your architecture does _NOT_ use the Linux
> - *  page-tables natively.
> - *
>   *  MMU_GATHER_NO_RANGE
>   *
>   *  Use this if your architecture lacks an efficient flush_tlb_range().
> @@ -203,6 +196,24 @@ extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
>  
>  #endif /* CONFIG_MMU_GATHER_TABLE_FREE */
>  
> +#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
> +
> +/*
> + * This allows an architecture that does not use the linux page-tables for
> + * hardware to skip the TLBI when freeing page tables.
> + */
> +#ifndef tlb_needs_table_invalidate
> +#define tlb_needs_table_invalidate() (true)
> +#endif
> +
> +#else
> +
> +#ifdef tlb_needs_table_invalidate
> +#error tlb_needs_table_invalidate() requires MMU_GATHER_RCU_TABLE_FREE
> +#endif
> +
> +#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
> +
>  #ifndef CONFIG_MMU_GATHER_NO_GATHER
>  /*
>   * If we can't allocate a page to make a big batch of page pointers
> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> index 9d103031568d..a3538cb2bcbe 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -177,14 +177,14 @@ static void tlb_remove_table_free(struct mmu_table_batch *batch)
>   */
>  static inline void tlb_table_invalidate(struct mmu_gather *tlb)
>  {
> -#ifndef CONFIG_MMU_GATHER_NO_TABLE_INVALIDATE
> -	/*
> -	 * Invalidate page-table caches used by hardware walkers. Then we still
> -	 * need to RCU-sched wait while freeing the pages because software
> -	 * walkers can still be in-flight.
> -	 */
> -	tlb_flush_mmu_tlbonly(tlb);
> -#endif
> +	if (tlb_needs_table_invalidate()) {
> +		/*
> +		 * Invalidate page-table caches used by hardware walkers. Then
> +		 * we still need to RCU-sched wait while freeing the pages
> +		 * because software walkers can still be in-flight.
> +		 */
> +		tlb_flush_mmu_tlbonly(tlb);
> +	}
>  }
>  
>  static void tlb_remove_table_one(void *table)

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