linux-kernel - Re: [PATCH v4 4/5] mm: hugetlb: fix missing cache flush in hugetlb_mcopy_atomic

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Date:   Wed, 9 Feb 2022 10:59:20 -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 4/5] mm: hugetlb: fix missing cache flush in
 hugetlb_mcopy_atomic_pte()

On 2/7/22 23:36, Muchun Song wrote:
> folio_copy() will copy the data from one page to the target page, then
> the target page will be mapped to the user space address, which might
> have an alias issue with the kernel address used to copy the data from
> the page to.  There are 2 ways to fix this issue.
> 
>  1) insert flush_dcache_page() after folio_copy().
>  2) replace folio_copy() with copy_user_huge_page() which already
>     considers the cache maintenance.
> 
> We chose 2) way to fix the issue since architectures can optimize this
> situation.
> 
> Fixes: 8cc5fcbb5be8 ("mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/hugetlb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Thanks!  This will also make backports easier.

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz