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 BCDBA30BBBF for ; Mon, 11 May 2026 07:17:31 +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=1778483851; cv=none; b=e/p5AYG6alvhiCgNhmjimm28sk7I3wSPFg8mnpzGlhwPYWd1SQez5ZroRcXJqNk938POXwFVBpHNdtpIEGA+5S4JJ2Wbjm3W7i+Ffw08aS1wl0jZ7k6EhPPOATNnvVL/GmqBg6sEIhjo5dZUB5P2glTC6UaA22cSL8hDdF9u3eE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778483851; c=relaxed/simple; bh=LkpLtBg7oCb43ClpBPUq4iq9i0Tn++YKd0G4AX2wqqg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tLl7E6pu6xGYGcpLVjhY8Qe0xZBTLNKe2bkfAFRaGb1TJlS1fpfeAI6wYLlUQX4Ia9LA9pHAJiiDnXFb4/mgXtViDlezTO7w/4cWJXLLyBsmjoqWlbxmac4xRzZ5h9gZzM6sIdSuIqMAP9jRDm/CUdzNF9zCO1t/ZyTmWF/O0ds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pRtc6Wve; 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="pRtc6Wve" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D1BB6C2BCB0; Mon, 11 May 2026 07:17:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778483851; bh=LkpLtBg7oCb43ClpBPUq4iq9i0Tn++YKd0G4AX2wqqg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pRtc6WveBLKgmpEpXQlwQ+gEzXNOv+ajONlpwi+nkmOlVJUoC5ECxOupiLcnpWqhs n3iIJbuMtuWIimGSuvnO4rLTxn8AgPTAb3n1LpR0/5ROvcQECPylEEb0dNjvidOfwi pfzNs0XhViQaQHvYKMKE4mz+M+eIY8ngqM470wieRlTTwDi0nYYPWwn7IWAFRcmfMk u/Bn6EQGYr6KWvcmwIW9ulyhhJ+GhtGO3S9im9/+UYILdDYvK/UHSJezRzcQkE8LDm eaOwj62qOJwSvjyDo4EwFmIXRuO/b6nosl/vSIS+PbrMPIpdKwsi1hL3P7PpksKosJ TGuQCiOyz7ccA== Message-ID: Date: Mon, 11 May 2026 09:17:27 +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 v2] 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: <20260511065701.799006-1-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 5/11/26 08:57, 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 -EINVAL early when > hstart > hend. > > madvise(PMD-aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); Ok, so providing a PMD-aligned address as start will result in 0 and a non-aligned address will result in -EINVAL. Didn't Lorenzo agree that just returning 0 in both cases would be clearer? But I might have misunderstood it. That would also make the code easier ... > > 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 > > --- > 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 | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 28a843f30b32..36baab17f098 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2837,6 +2837,15 @@ 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 -EINVAL; > + > + if (hstart == hend) > + return 0; > + ... as it would simply be: /* Nothing to collapse. */ if (hstart >= hend) return 0; @Lorenzo, or do we want to keep the (questionable : ) ) existing behavior? -- Cheers, David