From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755768AbbJHJoU (ORCPT ); Thu, 8 Oct 2015 05:44:20 -0400 Received: from mail-lb0-f173.google.com ([209.85.217.173]:35987 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755725AbbJHJoO (ORCPT ); Thu, 8 Oct 2015 05:44:14 -0400 Subject: Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support To: "Michael S. Tsirkin" References: <20151006174648-mutt-send-email-mst@redhat.com> <5613E75E.1040002@scylladb.com> <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> <56160039.4090901@scylladb.com> <20151008073246.GA19331@redhat.com> <56162D66.2030205@scylladb.com> <20151008114841-mutt-send-email-mst@redhat.com> Cc: 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 From: Avi Kivity Message-ID: <56163AE9.6020000@scylladb.com> Date: Thu, 8 Oct 2015 12:44:09 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151008114841-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/08/2015 12:16 PM, Michael S. Tsirkin wrote: > On Thu, Oct 08, 2015 at 11:46:30AM +0300, Avi Kivity wrote: >> >> On 10/08/2015 10:32 AM, Michael S. Tsirkin wrote: >>> On Thu, Oct 08, 2015 at 08:33:45AM +0300, Avi Kivity wrote: >>>> It is good practice to defend against root oopsing the kernel, but in some >>>> cases it cannot be achieved. >>> Absolutely. That's one of the issues with these patches. They don't even >>> try where it's absolutely possible. >>> >> Are you referring to blocking the maps of the msix BAR areas? > For example. There are more. I listed some of the issues on the mailing > list, and I might have missed some. VFIO has code to address all this, > people should share code to avoid duplication, or at least read it > to understand the issues. All but one of those are unrelated to the patch that adds msix support. > >> I think there is value in that. The value is small because a >> corruption is more likely in the dynamic memory responsible for tens >> of millions of DMA operations per second, rather than a static 4K >> area, but it exists. > There are other bugs which will hurt e.g. each time application does not > exit gracefully. uio_pci_generic disables DMA when the device is removed, so we're safe here, at least if files are released before the address space. > > But well, heh :) That's precisely my feeling about the whole "running > userspace drivers without an IOMMU" project. The value is small > since modern hardware has fast IOMMUs, but it exists. > For users that don't have iommus at all (usually because it is taken by the hypervisor), it has great value. I can't comment on iommu overhead; for my use case it is likely negligible and we will use an iommu when available; but apparently it matters for others.