From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 72F67388898; Mon, 6 Jul 2026 08:46:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783327567; cv=none; b=Pocj3/7MJ/ynqBtahT9GwD7p6litojvnTSeBlibfjZYrHAt3Y+iqVmpXicvjemb9fGieEgpm1ckjbyXVtU2yfImZVaIfr/tHevTd7rvONGA2cIOKb5y+d6q78hDXE9I3R4xCAe9HBuf0FxUW9pIihvmAT4Q9aCt5P8x5t6IQxs0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783327567; c=relaxed/simple; bh=yVfJ7vYaLxMKYQ23eZ8ZVLgi3CuLhcXCzf/o4zL5Ehg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mW5DvTa7ujv+X05IxCGBK1MYKcJz5WgdH2h5UipBJftfrMYNIs24eKmyMTYziG6g1MCExKmgvt8fVxS6iPW84bfS7b02hokOsl1nBNno/TdiVFp49pgQzGnAQlddJm++59W//m6M4Knbq/h5xKj9kHrOsS8KpIXixJUDjYIJzEA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VoNyyimY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VoNyyimY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9ED01F000E9; Mon, 6 Jul 2026 08:45:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783327556; bh=+VphFpucmenCRxzAqf6GCG3ouKRkPe9LBUQD12MWcpw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VoNyyimYnqqKLu1tQ9fTHSAp21AMnYBuiWyDfCJxhaM5/Kel8HyLFCw14x1s78N9U 7mGtgGN7PQ4XmdHlIMaW/7mlNyN/cMHkDlR8PbVdbyty6JdKay20g0qf+oHdS6g7BD uF9eg8bFVbc42WPLvi/yhsVBGSO6LkgMOTX2l+QzthLuq25fpiD6WwgLlbBL/WWC2U kdApDETEjy1WcUFc6A2sdKhZdnKGL20lVZikzBik4ow8GBgILpM6f0eCBgmOBqBrF4 hqE4J+OoveSZBRXmoWaSnTu/fspZaLo9MMP1OudEZa2PkV/QKRUvIlQW0v+WLjL8KI c0u/RfKS2F/2g== Message-ID: <4b4e8007-3747-457a-85cc-d1003e1c8fe2@kernel.org> Date: Mon, 6 Jul 2026 10:45:47 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/6] arm64: make huge_ptep_get handled unaligned addresses To: Dev Jain , Andrew Morton Cc: muchun.song@linux.dev, osalvador@suse.de, ljs@kernel.org, liam@infradead.org, riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, apopple@nvidia.com, rcampbell@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, ak@linux.intel.com, nao.horiguchi@gmail.com, mel@csn.ul.ie, j-nomura@ce.jp.nec.com, pfalcato@suse.de, tglx@kernel.org, dave.hansen@intel.com, jpoimboe@kernel.org, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20260703114202.365553-1-dev.jain@arm.com> <20260703114202.365553-2-dev.jain@arm.com> <20260705003559.8b124d2b94b685cc2e4e77ae@linux-foundation.org> <8fdbe0d6-87fd-441c-b6d2-baac380f6fb3@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/5/26 10:08, Dev Jain wrote: > > > On 05/07/26 1:05 pm, Andrew Morton wrote: >> On Fri, 3 Jul 2026 11:41:54 +0000 Dev Jain wrote: >> >>> huge_ptep_get() can be handed a virtual address pointing to the middle of >>> a contpmd/contpte mapped hugetlb folio (examples of callers are >>> pagemap_hugetlb_range, page_mapped_in_vma). >>> >>> The arm64 helper rewalks the pgtables in find_num_contig to answer whether >>> the huge pte we have maps a contpmd or a contpte hugetlb folio, and >>> returns CONT_PMDS or CONT_PTES, so that it can collect a/d bits over the >>> contiguous ptes. We can falsely return CONT_PTES instead of CONT_PMDS >>> if the addr is not aligned. >>> >>> Fix this by aligning the pmdp pointer down to a contpmd base before >>> checking equality with the passed huge pte pointer, to correctly answer >>> whether the huge pte is the base of a contpmd block. >>> >>> Fixes: 29cb80519689 ("arm64: hugetlb: Cleanup huge_pte size discovery mechanisms") >>> Cc: stable@vger.kernel.org >> >> Please describe the userspace-visible effects of bugs when fixing them. >> Particularly when cc:stable is proposed. Thanks. > > Forgot for this one. It should be, on systems where CONT_PTES != CONT_PMDS > (meaning page size is 16K) we could collect excess a/d bit state, meaning > extra work for the kernel. Even worse, right? We could walk 128 entries, when we really should just walk 16 (IIRC) entries, possibly reading garbage or even worse, into a memory hole at the end of memory? -- Cheers, David