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 30EB32F2607; Fri, 8 May 2026 12:27:41 +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=1778243262; cv=none; b=kxMQvXzco2rAUkPTNeELIYadca+H5wG93KtTFZ/Ud6KF727shkKSDAepXNPEkKLQhTG5yUWImizP4SBjdbRZVmN91VZiu8kVnvfztSJW+TxbRsefZt9RoRAX2L4lH6YLcx1Uq1Ss/xY2rckd8pLcZjk6wHgVJBK+sJJxU771Y24= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778243262; c=relaxed/simple; bh=ma++l05+jUjyVj+lcNXmwxDuxjpw7p6B1P8IKC8yMQM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dyiH4+YIwhqm26BIqmPV+iUj8ibgzyLqnf62pEYyWgZMo3j0SRh5PoAjB3QBQVfOqwzrXiS61Uvlgd4nZ5qkvdykDR4MXsj2nWkNAY2IwyTQyFLjbfeIgFCZ14NpI9+NlFy81gYCzDuC6e5DWcIMf6tEE3ZAgDdTwLJE3eHqm2U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WCEWqKKR; 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="WCEWqKKR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 628E5C2BCB8; Fri, 8 May 2026 12:27:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778243261; bh=ma++l05+jUjyVj+lcNXmwxDuxjpw7p6B1P8IKC8yMQM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WCEWqKKRcUw+sjbMY4GB6hIhqhRig1T9LBpWmxd+nA8f2RNcGBllNRagKqI5FzPkN 26WsO52bPsw5CHqjgtS4Rb3u2xUKya8vRxfVeFNKd2KLSLATsgfDBq4hpeNNIGXjZ8 2PO/vCswnxE0EQxQfrGL6LXYvtSayT9AeTQQOonJB5Ru/dqN2pcozNQcOwxcSJKQf2 GNvCRoso9B+/d6WwdVo4BS3ASXlLDzKauJCdFBiNLDBYCqY52n0jXnZLa+JiGGt0TQ GkErbG4t1NjoO/5a6oA4L8mPV3eO5mJDGDKtOE4Ufpkawu0K1TjSQmla59Tw4OqsG9 jEniXbBkz1QTA== Message-ID: <9eea2afb-8c35-47eb-b1de-6a08503c9679@kernel.org> Date: Fri, 8 May 2026 14:27:37 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/khugepaged: fix spurious -EINVAL from sub-PMD MADV_COLLAPSE range To: Chen Wandun , akpm@linux-foundation.org, ljs@kernel.org, shuah@kernel.org, zokeefe@google.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20260507070558.3064142-1-chenwandun@lixiang.com> <20260507070558.3064142-2-chenwandun@lixiang.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 5/7/26 09:05, Chen Wandun wrote: > madvise_collapse() computes the THP-aligned window: > > hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK /* round up */ > hend = end & HPAGE_PMD_MASK /* round down */ > > Previously this was done after kmalloc_obj(), so problem arose when > the range contained no complete PMD-aligned window (hstart >= hend). > > When hstart > hend, (hend - hstart) wraps unsigned to a huge value, the > final comparison fails and -EINVAL is returned instead of 0. Consider > two single-page calls on a 2 MiB-aligned address: > > /* hstart == hend == aligned -> 0 == 0 -> returns 0 */ > madvise(aligned, PAGE_SIZE, MADV_COLLAPSE); > > /* hstart = aligned + 2MiB, hend = aligned > * (hend - hstart) wraps unsigned -> returns -EINVAL */ > madvise(aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); > > Both calls cover less than one THP and collapse nothing; both should > return 0. Okay, so we talk about a "userspace is being stupid" scenario. > > In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() were all > called before discovering there was nothing to do, only for the code > to kfree() and return immediately after. Just a comment as you motivate here why this is suboptimal: we do not care about a "userspace is being stupid" scenario being fast. > > Fix both by computing hstart/hend after thp_vma_allowable_order() but > before kmalloc_obj(), and returning 0 early when hstart >= hend. > > Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") Fixes: is likely ok, but I don't think we want to treat this as a hotfix or CC stable. > Signed-off-by: Chen Wandun > --- > mm/khugepaged.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index b8452dbdb043..92473d93e837 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2836,6 +2836,12 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER)) > return -EINVAL; > > + hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; > + hend = end & HPAGE_PMD_MASK; > + > + if (hstart >= hend) > + return 0; > + > cc = kmalloc_obj(*cc); > if (!cc) > return -ENOMEM; > @@ -2845,9 +2851,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > mmgrab(mm); > lru_add_drain_all(); > > - hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; > - hend = end & HPAGE_PMD_MASK; > - > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > enum scan_result result = SCAN_FAIL; > In general, LGTM, but see for conflict: https://lore.kernel.org/all/20260409014323.2385982-1-ye.liu@linux.dev/ -- Cheers, David