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 EBB443D4138 for ; Wed, 13 May 2026 07:24:54 +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=1778657095; cv=none; b=j2/tb4+GQ/6yPV5ErYjZPZUnbu2/cMMUjjVvLkRp4qrXp2a/h3KFtd+v0B2UTCpmKGFM5XJK4GfG/yRXCsEokrm3fVMcgCRkugH492HEPbqzmqJP2+5jI6AT2cykT4V6w38t4bJqJYa/XfdXbVGiFJz41uQtN2meAUpomB4psik= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778657095; c=relaxed/simple; bh=dpHgGWbl4XrEZM7XmV0lYceMvJqpvt/MbCc9MMZHWMQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AKXKs5gGbpBiTpkUvjAbHJj2MuHio7qsu0ygwJouxnSz2WmF4P/Jmh2Yj429D4A+KHg4D8akMamTc7qZxRAuxRIcLC72GmWe/31bQRjOYNf4oVsThZndBbmqSlIozKsBo8/bn7/+mkWUcNdTwyuYQ/dfsDxVZSD2yvcktsKp9a4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ppxkSl2N; 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="ppxkSl2N" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61F04C2BCC6; Wed, 13 May 2026 07:24:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778657094; bh=dpHgGWbl4XrEZM7XmV0lYceMvJqpvt/MbCc9MMZHWMQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ppxkSl2N1TcSTxMaEht8arj5fuxglVI3CVBypZ0HviR9Q0DE0YMUk453T2bV16/cF mGaSMjpdT6WEvsvV8YeCxAiUDXn68edwaYKmBDzXdAmejvMcxd2BbrnzQMFgV5SKMm w9Ua/lMgzfZxEFS/wxfGws98jOVsxG8Go6hU3Hk3IrOfqZrKYKFZVB5l3v2kfZyaHT 4Uw0lticu1EpjxqMHA/S3RQAIbp+hE91oHIJcJ7qTv31QoAgAXNW913Bjx5+Ksfv13 26e+lefiHNIEoSoXNxXncDHQvvg+O7ZWmcOPNLEJTHTmB9/sO+6OI+TD6yihZx9Zwn x458dlZS7FvTQ== Message-ID: <3fbd1959-8619-4c10-b191-fb7b4ba029ff@kernel.org> Date: Wed, 13 May 2026 09:24:49 +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] mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE To: Wandun Chen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev References: <20260513055428.1664898-1-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 5/13/26 07:54, Wandun Chen wrote: > From: Chen Wandun > > madvise_collapse() computes the THP-aligned window: > > hstart = ALIGN(start, HPAGE_PMD_SIZE); /* round up */ > hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); /* round down */ > > The following case will cause hstart > hend, and result in underflow > in the return statement, avoid it by returning zero early when > hstart > hend. The return value is due to input is valid to madvise(), > and there is nothing to collapse. > > madvise(PMD-aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); > > In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() are > unnecessary when hstart == hend, so skip these operations by > returning early too. > > Signed-off-by: Chen Wandun > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David