From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f43.google.com (mail-pa0-f43.google.com [209.85.220.43]) by kanga.kvack.org (Postfix) with ESMTP id 5B07A6B0038 for ; Wed, 22 Oct 2014 16:13:09 -0400 (EDT) Received: by mail-pa0-f43.google.com with SMTP id eu11so1713pac.2 for ; Wed, 22 Oct 2014 13:13:09 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id qn8si15105055pab.104.2014.10.22.13.13.08 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Oct 2014 13:13:08 -0700 (PDT) Date: Wed, 22 Oct 2014 13:13:08 -0700 From: Andrew Morton Subject: Re: [PATCH] mm, hugetlb: correct bit shift in hstate_sizelog Message-Id: <20141022131308.361a72ba7c6fbf1bd778445a@linux-foundation.org> In-Reply-To: <5447FC6E.2000207@oracle.com> References: <1413915307-20536-1-git-send-email-sasha.levin@oracle.com> <544743D6.6040103@samsung.com> <20141022114437.72eb61ce3e2348c52ab3d1db@linux-foundation.org> <5447FC6E.2000207@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Sasha Levin Cc: Andrey Ryabinin , n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, mgorman@suse.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Wed, 22 Oct 2014 14:50:22 -0400 Sasha Levin wrote: > On 10/22/2014 02:44 PM, Andrew Morton wrote: > > On Wed, 22 Oct 2014 09:42:46 +0400 Andrey Ryabinin wrote: > > > >> > On 10/21/2014 10:15 PM, Sasha Levin wrote: > >>> > > hstate_sizelog() would shift left an int rather than long, triggering > >>> > > undefined behaviour and passing an incorrect value when the requested > >>> > > page size was more than 4GB, thus breaking >4GB pages. > >> > > >>> > > > >>> > > Signed-off-by: Sasha Levin > >>> > > --- > >>> > > include/linux/hugetlb.h | 3 ++- > >>> > > 1 file changed, 2 insertions(+), 1 deletion(-) > >>> > > > >>> > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > >>> > > index 65e12a2..57e0dfd 100644 > >>> > > --- a/include/linux/hugetlb.h > >>> > > +++ b/include/linux/hugetlb.h > >>> > > @@ -312,7 +312,8 @@ static inline struct hstate *hstate_sizelog(int page_size_log) > >>> > > { > >>> > > if (!page_size_log) > >>> > > return &default_hstate; > >>> > > - return size_to_hstate(1 << page_size_log); > >>> > > + > >>> > > + return size_to_hstate(1UL << page_size_log); > >> > > >> > That still could be undefined on 32-bits. Either use 1ULL or reduce SHM_HUGE_MASK on 32bits. > >> > > > But > > > > struct hstate *size_to_hstate(unsigned long size) > > True, but "(1 << page_size_log)" produces an integer rather than long because "1" > is an int and not long. My point is that there's no point in using 1ULL because size_to_hstate() will truncate it anyway. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org