From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A275C3A5A6 for ; Tue, 27 Aug 2019 16:24:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE5A6214DA for ; Tue, 27 Aug 2019 16:24:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730038AbfH0QYh (ORCPT ); Tue, 27 Aug 2019 12:24:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41836 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726522AbfH0QYh (ORCPT ); Tue, 27 Aug 2019 12:24:37 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 320803082126; Tue, 27 Aug 2019 16:24:36 +0000 (UTC) Received: from x1.home (ovpn-116-99.phx2.redhat.com [10.3.116.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8A2295DC18; Tue, 27 Aug 2019 16:24:35 +0000 (UTC) Date: Tue, 27 Aug 2019 10:24:35 -0600 From: Alex Williamson To: Parav Pandit Cc: Cornelia Huck , Jiri Pirko , "kwankhede@nvidia.com" , "davem@davemloft.net" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs Message-ID: <20190827102435.7bd30ef3@x1.home> In-Reply-To: References: <20190826204119.54386-1-parav@mellanox.com> <20190826204119.54386-3-parav@mellanox.com> <20190827122928.752e763b.cohuck@redhat.com> <20190827132946.0b92d259.cohuck@redhat.com> <20190827092855.29702347@x1.home> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 27 Aug 2019 16:24:36 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, 27 Aug 2019 16:13:27 +0000 Parav Pandit wrote: > > -----Original Message----- > > From: Alex Williamson > > Sent: Tuesday, August 27, 2019 8:59 PM > > To: Cornelia Huck > > Cc: Parav Pandit ; Jiri Pirko ; > > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org; linux- > > kernel@vger.kernel.org; netdev@vger.kernel.org > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all mdevs > > > > On Tue, 27 Aug 2019 13:29:46 +0200 > > Cornelia Huck wrote: > > > > > On Tue, 27 Aug 2019 11:08:59 +0000 > > > Parav Pandit wrote: > > > > > > > > -----Original Message----- > > > > > From: Cornelia Huck > > > > > Sent: Tuesday, August 27, 2019 3:59 PM > > > > > To: Parav Pandit > > > > > Cc: alex.williamson@redhat.com; Jiri Pirko ; > > > > > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org; > > > > > linux- kernel@vger.kernel.org; netdev@vger.kernel.org > > > > > Subject: Re: [PATCH 2/4] mdev: Make mdev alias unique among all > > > > > mdevs > > > > > > > > > > On Mon, 26 Aug 2019 15:41:17 -0500 Parav Pandit > > > > > wrote: > > > > > > > > > > > Mdev alias should be unique among all the mdevs, so that when > > > > > > such alias is used by the mdev users to derive other objects, > > > > > > there is no collision in a given system. > > > > > > > > > > > > Signed-off-by: Parav Pandit > > > > > > --- > > > > > > drivers/vfio/mdev/mdev_core.c | 5 +++++ > > > > > > 1 file changed, 5 insertions(+) > > > > > > > > > > > > diff --git a/drivers/vfio/mdev/mdev_core.c > > > > > > b/drivers/vfio/mdev/mdev_core.c index e825ff38b037..6eb37f0c6369 > > > > > > 100644 > > > > > > --- a/drivers/vfio/mdev/mdev_core.c > > > > > > +++ b/drivers/vfio/mdev/mdev_core.c > > > > > > @@ -375,6 +375,11 @@ int mdev_device_create(struct kobject *kobj, > > struct > > > > > device *dev, > > > > > > ret = -EEXIST; > > > > > > goto mdev_fail; > > > > > > } > > > > > > + if (tmp->alias && strcmp(tmp->alias, alias) == 0) { > > > > > > > > > > Any way we can relay to the caller that the uuid was fine, but > > > > > that we had a hash collision? Duplicate uuids are much more obvious than > > a collision here. > > > > > > > > > How do you want to relay this rare event? > > > > Netlink interface has way to return the error message back, but sysfs is > > limited due to its error code based interface. > > > > > > I don't know, that's why I asked :) > > > > > > The problem is that "uuid already used" and "hash collision" are > > > indistinguishable. While "use a different uuid" will probably work in > > > both cases, "increase alias length" might be a good alternative in > > > some cases. > > > > > > But if there is no good way to relay the problem, we can live with it. > > > > It's a rare event, maybe just dev_dbg(dev, "Hash collision creating alias \"%s\" > > for mdev device %pUl\n",... > > > Ok. > dev_dbg_once() to avoid message flood. I'd suggest a rate-limit rather than a once. The fact that the kernel may have experienced a collision at some time in the past does not help someone debug why they can't create a device now. The only way we're going to get a flood is if a user sufficiently privileged to create mdev devices stumbles onto a collision and continues to repeat the same operation. That falls into shoot-yourself-in-the-foot behavior imo. Thanks, Alex