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Date:   Wed, 9 Feb 2022 11:07:07 -0800
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Subject: Re: [PATCH v4 3/5] mm: hugetlb: fix missing cache flush in
 copy_huge_page_from_user()
Content-Language: en-US
To:     Muchun Song <songmuchun@bytedance.com>, akpm@linux-foundation.org,
        zi.yan@cs.rutgers.edu, kirill.shutemov@linux.intel.com,
        rientjes@google.com, lars.persson@axis.com, ziy@nvidia.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        duanxiongchun@bytedance.com, fam.zheng@bytedance.com
References: <20220208073617.70342-1-songmuchun@bytedance.com>
 <20220208073617.70342-4-songmuchun@bytedance.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
In-Reply-To: <20220208073617.70342-4-songmuchun@bytedance.com>
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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@oracle.com>

-- 
Mike Kravetz

> 
> Fixes: fa4d75c1de13 ("userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support")
> Signed-off-by: Muchun Song <songmuchun@bytedance.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;