From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 88A2A21772A; Thu, 26 Mar 2026 09:18:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774516698; cv=none; b=fMLLjfz89meUhPzoEkoBcDUWhtRmx374AW2PZPCUx3riCquTWQubnTm/UoFhaAuc+84qUNYs3ACrDD1Vlk8ySFlq/5USXcjyEtUXkPCH3ls0D11zYvd5MO1xTOrB+805lX+XMtFugUXbNC+PL6q4HgnIRH0vtSnv53wTpDVIBUI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774516698; c=relaxed/simple; bh=NB9e1yRv7pQYfcNDqbhIQZdzYe4Yg+3OBRyNgSet0K0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KswolFzCy6vKAtoMXFEnM3tyl0+rydmRGGXh2qaGZCqtYYjHEnGSziDqEXB78d7EsDV+mJi6hscCaNRGGu90IY7Ol5QRycZ8KCRiYoubXnAqVV0e2nC8o8aznulVex3axwkDbK0iWSOmQkVLpJ+r66K60HVOiyKrD2trEh5Y2nw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=r57v5qpD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="r57v5qpD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6160DC19423; Thu, 26 Mar 2026 09:18:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774516698; bh=NB9e1yRv7pQYfcNDqbhIQZdzYe4Yg+3OBRyNgSet0K0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=r57v5qpDP1JpL+YD/QaJaQgZtR5duvUUh90CXCPBJWiBbbSdK1/4QS/jk4W5Fm8pb ybMjtmNodPUshgbu2mGVTo7i4SunYaneQLWeZX6F2Fy0SvXxmPSRBEwsnvR+LnBvbm eFl2TYr+EMQZBFfaQSC+mVmACiLlvxpSL93C8f703OsXLv6CiWXRypuzJwj2oOpfFl b4qFJAUKNQrV5pmJIR7ibXzpk4groEy0hej/wz07tzOiAbyW5PY9UR/FYCe9AZPKDb HYGVATtm1OkvfnIE60Pnd8OcFtCwG2t0XJTFh0ByY2C+hUcJUaEF3IOCKyrUqYAOFc pTDUCaouS+UDw== Message-ID: <9ec9edd1-0f4c-4da2-ae78-0e7b251a9e25@kernel.org> Date: Thu, 26 Mar 2026 10:18:09 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm/userfaultfd: fix hugetlb fault mutex hash calculation To: jane.chu@oracle.com, Andrew Morton , Jianhui Zhou , Muchun Song , Oscar Salvador , Mike Rapoport Cc: Peter Xu , Andrea Arcangeli , Mike Kravetz , SeongJae Park , Hugh Dickins , Sidhartha Kumar , Jonas Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com References: <20260306140332.171078-1-jianhuizzzzz@gmail.com> <20260310110526.335749-1-jianhuizzzzz@gmail.com> <12e822c4-a4f2-4447-80b9-2eec35a03188@oracle.com> <20260324170311.dc5b54fe0765f2e680e3cc90@linux-foundation.org> <1075f7a0-232f-4268-94b3-573d11c4203f@kernel.org> <67287b4a-7b93-4061-af4d-65e4a163c61c@oracle.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/26/26 00:46, jane.chu@oracle.com wrote: > Hi, David, > > On 3/25/2026 1:49 AM, David Hildenbrand (Arm) wrote: > [..] [...] >> >> But it raises the question: >> >> (1) should be convert all that to just operate on the ordinary index, >> such that we don't even need hugetlb_linear_page_index()? That would be >> an addon patch. >> > > Do you mean to convert all callers of hugetlb_linear_page_index() and > vma_hugepcache_offset() to use index and huge_page_order(h) ? > May I add, to improve readability, rename the huge-page-granularity > 'idx' to huge_idx or hidx ? What I meant is that we change all hugetlb code to use the ordinary idx. It's a bigger rework. For example, we'd be getting rid of filemap_lock_hugetlb_folio() completely and simply use filemap_lock_folio. As one example: @@ -657,10 +657,9 @@ static void hugetlbfs_zero_partial_page(struct hstate *h, loff_t start, loff_t end) { - pgoff_t idx = start >> huge_page_shift(h); struct folio *folio; - folio = filemap_lock_hugetlb_folio(h, mapping, idx); + folio = filemap_lock_folio(mapping, start >> PAGE_SHIFT); if (IS_ERR(folio)) return; Other parts are more tricky, as we have to make sure that we get an idx that points at the start of the folio. Likely such a conversion could be done incrementally. But it's a bit of work. We'd be getting rid of some more hugetlb special casing. An alternative is passing in an address into hugetlb_linear_page_index(), just letting it do the calculation itself (it can get the hstate from the mapping). > >> (2) Alternatively, could we replace all users of vma_hugecache_offset() >> by the much cleaner hugetlb_linear_page_index() ? >> > > The difference between the two helpers is hstate_vma() in the latter > that is about 5 pointer de-references, not sure of any performance > implication though.  hstate_vma() is really just hstate_file(vma->vm_file)-> hstate_inode(file_inode(f))->HUGETLBFS_SB(i->i_sb)->hstate; So some pointer chasing. hard to believe that this would matter in any of this code :) > At minimum, we could have >   hugetlb_linear_page_index(vma, addr) >   -> __hugetlb_linear_page_index(h, vma, addr) > basically renaming vma_hugecache_offset(). I would only do that if it's really required for performance. -- Cheers, David