linux-kernel - Re: [PATCH v4 3/5] mm: hugetlb: fix missing cache flush in copy_huge_page_from

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Message-ID: <d78d6e56-1879-94c8-dc28-06431e583a77@oracle.com>
Date:   Wed, 9 Feb 2022 11:07:07 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>, akpm@...ux-foundation.org,
        zi.yan@...rutgers.edu, kirill.shutemov@...ux.intel.com,
        rientjes@...gle.com, lars.persson@...s.com, ziy@...dia.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com, fam.zheng@...edance.com
Subject: Re: [PATCH v4 3/5] mm: hugetlb: fix missing cache flush in
 copy_huge_page_from_user()

On 2/7/22 23:36, Muchun Song wrote:
> The userfaultfd calls copy_huge_page_from_user() which does not do
> any cache flushing for the target page.  Then the target page will
> be mapped to the user space with a different address (user address),
> which might have an alias issue with the kernel address used to copy
> the data from the user to.  Fix this issue by flushing dcache in
> copy_huge_page_from_user().

Quick question.

Should this also be done for the non-hugetlb case?  Take a look at the
routines __mcopy_atomic() and mcopy_atomic_pte().  Or, is that somehow
handled?

For this change,
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz

> 
> Fixes: fa4d75c1de13 ("userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/memory.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e8ce066be5f2..eb027da68aa7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5405,6 +5405,8 @@ long copy_huge_page_from_user(struct page *dst_page,
>  		if (rc)
>  			break;
>  
> +		flush_dcache_page(subpage);
> +
>  		cond_resched();
>  	}
>  	return ret_val;