linux-kernel - Re: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'

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Message-ID: <jdfdmwanxzi6udltiezoqli77kutoeuzodet6tsfyyu4sibbom@yxhycebnts6j>
Date:   Mon, 19 Jun 2023 14:35:15 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dri-devel@...ts.freedesktop.org, qemu-devel@...gnu.org,
        Vivek Kasireddy <vivek.kasireddy@...el.com>,
        Dongwon Kim <dongwon.kim@...el.com>,
        Junxiao Chang <junxiao.chang@...el.com>,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        jmarchan@...hat.com, muchun.song@...ux.dev,
        James Houghton <jthoughton@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'

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@...r.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

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