From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755582AbbJHMPa (ORCPT ); Thu, 8 Oct 2015 08:15:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57223 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752514AbbJHMP3 (ORCPT ); Thu, 8 Oct 2015 08:15:29 -0400 Date: Thu, 8 Oct 2015 15:15:20 +0300 From: "Michael S. Tsirkin" To: Gleb Natapov Cc: Avi Kivity , Alex Williamson , Vlad Zolotarov , Greg KH , linux-kernel@vger.kernel.org, hjk@hansjkoch.de, corbet@lwn.net, bruce.richardson@intel.com, avi@cloudius-systems.com, gleb@cloudius-systems.com, stephen@networkplumber.org, alexander.duyck@gmail.com Subject: Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support Message-ID: <20151008151147-mutt-send-email-mst@redhat.com> References: <1444157480.4059.67.camel@redhat.com> <5614C11B.6090601@scylladb.com> <1444235464.4059.169.camel@redhat.com> <56154AB4.1050509@scylladb.com> <20151007230553-mutt-send-email-mst@redhat.com> <20151008041913.GB13818@scylladb.com> <20151008074153.GB19331@redhat.com> <20151008075910.GD11716@scylladb.com> <20151008121727-mutt-send-email-mst@redhat.com> <20151008094508.GH11716@scylladb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151008094508.GH11716@scylladb.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 08, 2015 at 12:45:08PM +0300, Gleb Natapov wrote: > On Thu, Oct 08, 2015 at 12:38:28PM +0300, Michael S. Tsirkin wrote: > > On Thu, Oct 08, 2015 at 10:59:10AM +0300, Gleb Natapov wrote: > > > I do not remember this been an issue when uio_generic was accepted > > > into the kernel. The reason was because it meant to be accessible by root > > > only. > > > > No - because it does not need bus mastering. So it can be used safely > > with some devices. > > > It still can be used safely with same devices. This patch does not add any functionality that can be used safely. And for no good reason except it's a hassle. > Admittedly I did not look > close, but I am sure the patch does not enable bus mastering if MSI > interrupt is not requested. If not, well that can be fixed. But more > importantly it can be used unsafely in its current state. Not only can, > it is widely used so. > > > [mst@robin linux]$ git grep pci_set_master|wc -l 533 > > [mst@robin linux]$ git grep pci_enable|wc -l 1597 > > > > Looks like about 2/3 devices don't need to be bus masters. > > > > It's up to admin not to bind it to devices, and that is unfortunate, > > but manually binding an incorrect driver to a device is generally > > a hard problem to solve. > > > > > > There's also drivers/vfio/virqfd.c which deals > > > > with sending interrupts over eventfds correctly. > > > > > > > As opposite to this patch that deals with them incorrectly? In what way? > > > > cleanup on fd close is not handled. > > > Have you commented about this on the patch and it was not fixed? No - I only noticed this when I poked at VFIO to try and explain why it's not a good idea to duplicate its code. I'm sure there are more issues that we'll just have to re-discover the hard way if we do try. > -- > Gleb.