linux-kernel - Re: [PATCH 08/18] arm/tlb: Convert to generic mmu

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Message-ID: <20180926125405.GH2979@brain-police>
Date:   Wed, 26 Sep 2018 13:54:06 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     aneesh.kumar@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        npiggin@...il.com, linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        heiko.carstens@...ibm.com, riel@...riel.com
Subject: Re: [PATCH 08/18] arm/tlb: Convert to generic mmu_gather

On Wed, Sep 26, 2018 at 01:36:31PM +0200, Peter Zijlstra wrote:
> Generic mmu_gather provides everything that ARM needs:
> 
>  - range tracking
>  - RCU table free
>  - VM_EXEC tracking
>  - VIPT cache flushing
> 
> The one notable curiosity is the 'funny' range tracking for classical
> ARM in __pte_free_tlb().
> 
> Cc: Nick Piggin <npiggin@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/arm/include/asm/tlb.h |  255 ++-------------------------------------------
>  1 file changed, 14 insertions(+), 241 deletions(-)

[...]

>  static inline void
> -tlb_remove_pmd_tlb_entry(struct mmu_gather *tlb, pmd_t *pmdp, unsigned long addr)
> +__pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp, unsigned long addr)
>  {
> -	tlb_add_flush(tlb, addr);
> -}
> -
> -#define pte_free_tlb(tlb, ptep, addr)	__pte_free_tlb(tlb, ptep, addr)
> -#define pmd_free_tlb(tlb, pmdp, addr)	__pmd_free_tlb(tlb, pmdp, addr)
> -#define pud_free_tlb(tlb, pudp, addr)	pud_free((tlb)->mm, pudp)
> -
> -#define tlb_migrate_finish(mm)		do { } while (0)
> -
> -static inline void tlb_change_page_size(struct mmu_gather *tlb,
> -						     unsigned int page_size)
> -{
> -}
> -
> -static inline void tlb_flush_remove_tables(struct mm_struct *mm)
> -{
> -}
> +#ifdef CONFIG_ARM_LPAE
> +	struct page *page = virt_to_page(pmdp);
>  
> -static inline void tlb_flush_remove_tables_local(void *arg)
> -{
> +	pgtable_pmd_page_dtor(page);

The dtor() is a NOP for Arm, so I don't think you need too call it (and we
never call the ctor() afaict). I wonder if should be caring about this on
arm64...

Other than that:

Acked-by: Will Deacon <will.deacon@....com>

Will