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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 21 Jan 2019 11:10:44 -0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x0LBAhYe6881720 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 21 Jan 2019 11:10:43 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 471B6AE0BD; Mon, 21 Jan 2019 11:10:43 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A9E01AE09E; Mon, 21 Jan 2019 11:10:41 +0000 (GMT) Received: from rapoport-lnx (unknown [9.148.206.247]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Mon, 21 Jan 2019 11:10:41 +0000 (GMT) Date: Mon, 21 Jan 2019 13:10:39 +0200 From: Mike Rapoport To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Maya Gokhale , Jerome Glisse , Johannes Weiner , Martin Cracauer , Denis Plotnikov , Shaohua Li , Andrea Arcangeli , Pavel Emelyanov , Mike Kravetz , Marty McFadden , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH RFC 20/24] userfaultfd: wp: don't wake up when doing write protect References: <20190121075722.7945-1-peterx@redhat.com> <20190121075722.7945-21-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190121075722.7945-21-peterx@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 19012111-0020-0000-0000-000003094414 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19012111-0021-0000-0000-0000215A72A5 Message-Id: <20190121111039.GB26461@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-21_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=864 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901210088 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 21, 2019 at 03:57:18PM +0800, Peter Xu wrote: > It does not make sense to try to wake up any waiting thread when we're > write-protecting a memory region. Only wake up when resolving a write > protected page fault. Probably it would be better to make it default to wake up only when requested explicitly? Then we can simply disallow _DONTWAKE for uffd_wp and only use UFFDIO_WRITEPROTECT_MODE_WP as possible mode. > Signed-off-by: Peter Xu > --- > fs/userfaultfd.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 455b87c0596f..e54ab6076e13 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1771,6 +1771,7 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, > struct uffdio_writeprotect uffdio_wp; > struct uffdio_writeprotect __user *user_uffdio_wp; > struct userfaultfd_wake_range range; > + bool mode_wp, mode_dontwake; > > user_uffdio_wp = (struct uffdio_writeprotect __user *) arg; > > @@ -1786,17 +1787,19 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, > if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE | > UFFDIO_WRITEPROTECT_MODE_WP)) > return -EINVAL; > - if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) && > - (uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) > + > + mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP; > + mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE; > + > + if (mode_wp && mode_dontwake) > return -EINVAL; > > ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start, > - uffdio_wp.range.len, uffdio_wp.mode & > - UFFDIO_WRITEPROTECT_MODE_WP); > + uffdio_wp.range.len, mode_wp); > if (ret) > return ret; > > - if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) { > + if (!mode_wp && !mode_dontwake) { > range.start = uffdio_wp.range.start; > range.len = uffdio_wp.range.len; > wake_userfault(ctx, &range); > -- > 2.17.1 > -- Sincerely yours, Mike.