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 56BE62BD01B for ; Wed, 13 May 2026 09:24:10 +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=1778664250; cv=none; b=ObFb6HOYgw3TEQeDMPAESXaBsrgWWJz+metsZZizM1O2WdSHwQov/aaHbNmZKEme7mQdAR4cfQF7VsGGCXgDz8p8cY1Grx99USXL9vIdmO2JB5HVYE5zH3aRqgcpY9mCd9cI/zr/23ig00xRXM+6/2Q9FKbAqVQpUdICptCQsV4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778664250; c=relaxed/simple; bh=U4cfKROV64PvlEYkhn23spLaVTZ7LHG2wwR6srRFir8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=npoevNzD3AXCL/QsoftusPySL24YstGAK9NOBf1Cq9LnKtW0N56oDa4grbFog+pium5rIEl6OqOrQz5h2Y12dMzu1NAIhYahx+lO97JExFWbDdZKtRZFKzvJ1OnbKVuIi0b3Qy58IkscN2OX+gBNwYhED6dHhVINKDF0qQHFq/k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rVBVNUig; 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="rVBVNUig" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F72EC2BCB7; Wed, 13 May 2026 09:24:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778664250; bh=U4cfKROV64PvlEYkhn23spLaVTZ7LHG2wwR6srRFir8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rVBVNUigUVvlNY555mAOpCIiZjUGylqsFAp5Q5aD6+5HkauJsfJ9pzXhmAu0BC3mw o2bqU0D3x4NHWoPMVLd/QGgcZw3Ag/8REFdIbCixopegFo3Nkfvn8M+NxIsKK9E/Gm hAeyo3LnkJ7/9vIJZDfEttrK/VrE2OVHq1ZmARv/yYRptsbUc34O73uNPvSKA9bGq/ yhy5WFOMW1+QUEkpHOP1ZtG5vK1veprQdFKqYdOz/0EjnjYyg2fMyWo3Ssm8ExniuW 3F0GTrD+0tAKZuP28fKGInIFcu5OjyiKEO4Ty9dwWr6GILe1jPama5O/i7mP5CpYUQ MBIaRfZvKIGZA== Date: Wed, 13 May 2026 10:24:04 +0100 From: Lorenzo Stoakes To: Wandun Chen Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, david@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 Subject: Re: [PATCH v3] mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE Message-ID: References: <20260513055428.1664898-1-chenwandun@lixiang.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260513055428.1664898-1-chenwandun@lixiang.com> On Wed, May 13, 2026 at 01:54:28PM +0800, 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 LGTM, so: Reviewed-by: Lorenzo Stoakes Cheers, Lorenzo > --- > v2 --> v3: > - Return 0 when hstart > hend, suggested by David and Lorenzo. > > v1 --> v2: > - Rebase and resolve code conflict. > - Return -EINVAL when hstart > hend, suggested by Lorenzo. > - Drop Fixes tag, suggested by David and Lorenzo. > - Updated commit message to be more explicit, suggested by Lorenzo. > --- > mm/khugepaged.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 28a843f30b32..fd7e893c998d 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2837,6 +2837,12 @@ 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 = ALIGN(start, HPAGE_PMD_SIZE); > + hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); > + > + if (hstart >= hend) > + return 0; > + > cc = kmalloc_obj(*cc); > if (!cc) > return -ENOMEM; > @@ -2846,9 +2852,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > mmgrab(mm); > lru_add_drain_all(); > > - hstart = ALIGN(start, HPAGE_PMD_SIZE); > - hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); > - > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > enum scan_result result = SCAN_FAIL; > > -- > 2.43.0 >