linux-kernel - Re: [PATCH 1/2] mm: thp: fix wrong cache flush in remove_migration

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Date:   Fri, 21 Jan 2022 09:55:06 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: thp: fix wrong cache flush in remove_migration_pmd()

On 21 Jan 2022, at 3:13, Muchun Song wrote:

> The flush_cache_page() is supposed to be justified only if the page
> is already placed in process page table, and that is done right after
> flush_cache_page(). So using this interface is wrong. And there is
> no need to invalite cache since it was non-present before in
> remove_migration_pmd(). So just to remove it.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/huge_memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index f58524394dc1..45ede45b11f5 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3207,7 +3207,6 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
>  	if (pmd_swp_uffd_wp(*pvmw->pmd))
>  		pmde = pmd_wrprotect(pmd_mkuffd_wp(pmde));
>
> -	flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE);
>  	if (PageAnon(new))
>  		page_add_anon_rmap(new, vma, mmun_start, true);
>  	else
> @@ -3215,6 +3214,8 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
>  	set_pmd_at(mm, mmun_start, pvmw->pmd, pmde);
>  	if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new))
>  		mlock_vma_page(new);
> +
> +	/* No need to invalidate - it was non-present before */
>  	update_mmu_cache_pmd(vma, address, pvmw->pmd);
>  }
>  #endif

LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

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