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Date:   Mon, 19 Jun 2023 14:35:15 +0200
From:   Gerd Hoffmann <kraxel@redhat.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        dri-devel@lists.freedesktop.org, qemu-devel@nongnu.org,
        Vivek Kasireddy <vivek.kasireddy@intel.com>,
        Dongwon Kim <dongwon.kim@intel.com>,
        Junxiao Chang <junxiao.chang@intel.com>,
        kirill.shutemov@linux.intel.com, mhocko@suse.com,
        jmarchan@redhat.com, muchun.song@linux.dev,
        James Houghton <jthoughton@google.com>,
        David Hildenbrand <david@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        stable@vger.kernel.org
Subject: Re: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'
Message-ID: <jdfdmwanxzi6udltiezoqli77kutoeuzodet6tsfyyu4sibbom@yxhycebnts6j>
References: <20230608204927.88711-1-mike.kravetz@oracle.com>
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In-Reply-To: <20230608204927.88711-1-mike.kravetz@oracle.com>
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On Thu, Jun 08, 2023 at 01:49:27PM -0700, Mike Kravetz wrote:
> This effectively reverts commit 16c243e99d33 ("udmabuf: Add support
> for mapping hugepages (v4)").  Recently, Junxiao Chang found a BUG
> with page map counting as described here [1].  This issue pointed out
> that the udmabuf driver was making direct use of subpages of hugetlb
> pages.  This is not a good idea, and no other mm code attempts such use.
> In addition to the mapcount issue, this also causes issues with hugetlb
> vmemmap optimization and page poisoning.
> 
> For now, remove hugetlb support.
> 
> If udmabuf wants to be used on hugetlb mappings, it should be changed to
> only use complete hugetlb pages.  This will require different alignment
> and size requirements on the UDMABUF_CREATE API.
> 
> [1] https://lore.kernel.org/linux-mm/20230512072036.1027784-1-junxiao.chang@intel.com/
> 
> Fixes: 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Gerd Hoffmann <kraxel@redhat.com>