linux-kernel - Re: [PATCH 2/4] mm: mremap: use flush_pmd_tlb_range() in move_normal

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Message-ID: <ZMeVdcNcp76L8bOG@arm.com>
Date:   Mon, 31 Jul 2023 12:05:25 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mina Almasry <almasrymina@...gle.com>, kirill@...temov.name,
        joel@...lfernandes.org, william.kucharski@...cle.com,
        kaleshsingh@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm: mremap: use flush_pmd_tlb_range() in
 move_normal_pmd()

On Mon, Jul 31, 2023 at 03:48:27PM +0800, Kefeng Wang wrote:
> Archs may need to do special things when flushing thp tlb,
> so use the more applicable flush_pud_tlb_range() instead of
> flush_tlb_range().
> 
> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>  mm/mremap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 11e06e4ab33b..1883205fa22b 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -284,7 +284,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>  	VM_BUG_ON(!pmd_none(*new_pmd));
>  
>  	pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
> -	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
> +	flush_pmd_tlb_range(vma, old_addr, old_addr + PMD_SIZE);

I don't think that's correct for arm64. The assumption in the
flush_p*d_tlb_range() was that they are called only for block mappings
at that p*d level (and we use FEAT_TTL on arm64 indicating that the leaf
level is level 2 for pmd, 1 for pud). IIUC move_normal_pmd() is only
called for table pmds which would have a leaf level of 3 (the pte).

Same for the next patch doing the equivalent for the pud.

-- 
Catalin