From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751599Ab1HOBB5 (ORCPT ); Sun, 14 Aug 2011 21:01:57 -0400 Received: from ozlabs.org ([203.10.76.45]:56146 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937Ab1HOBBy (ORCPT ); Sun, 14 Aug 2011 21:01:54 -0400 From: Rusty Russell To: Sasha Levin Cc: linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] virtio-net: Read MAC only after initializing MSI-X In-Reply-To: <1313330252.2422.12.camel@sasha> References: <1313225461-24458-1-git-send-email-levinsasha928@gmail.com> <878vqw9007.fsf@rustcorp.com.au> <1313330252.2422.12.camel@sasha> User-Agent: Notmuch/0.5 (http://notmuchmail.org) Emacs/23.2.1 (i686-pc-linux-gnu) Date: Mon, 15 Aug 2011 09:55:26 +0930 Message-ID: <87vctz7c7d.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 14 Aug 2011 16:57:32 +0300, Sasha Levin wrote: > On Sun, 2011-08-14 at 12:23 +0930, Rusty Russell wrote: > > On Sat, 13 Aug 2011 11:51:01 +0300, Sasha Levin wrote: > > > The MAC of a virtio-net device is located at the first field of the device > > > specific header. This header is located at offset 20 if the device doesn't > > > support MSI-X or offset 24 if it does. > > > > Erk. This means, in general, we have to do virtio_find_single_vq or > > config->find_vqs before we examine any config options. > > > > Look at virtio_blk, which has the same error. > > > > Solutions in order of best to worst: > > (1) Enable MSI-X before calling device probe. This means reserving two > > vectors in virtio_pci_probe to ensure we *can* do this, I think. Michael? > > Do you mean reserving the vectors even before we probed the device for > MSI-X support? Wouldn't we need 3 vectors then? (config, input, output). We want three, but *need* two: see vp_find_vqs(). Also, the generic code doesn't know how many virtqueues we have on the device. > > (2) Ensure ordering of "find_vqs then access config space" statically. This > > probably means handing the vqs array to virtio_config_val, so noone > > can call it before they have their virtqueues. > > Just noticed that only virtio-blk uses virtio_config_val(), while the > others are still doing 'if(virtio_has_feature()) vdev->config->get()', > I'll send patches to fix that regardless of what we end up doing here. Thanks. > Did you want to pass the vq array to virtio_config_val() just to check > that they were already found? Not if we fix is using method #1... Thanks, Rusty.