From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation Date: Wed, 5 Sep 2012 22:16:57 +0300 Message-ID: <20120905191657.GA15868@redhat.com> References: <1346680277-5887-1-git-send-email-sjur.brandeland@stericsson.com> <20120903143018.GA5353@redhat.com> <20120903202737.GD6181@redhat.com> <87zk56e2xc.fsf@rustcorp.com.au> <20120905143558.GB10925@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Sjur =?iso-8859-1?Q?Br=E6ndeland?= Cc: Linus Walleij , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Amit Shah , Sjur =?iso-8859-1?Q?Br=E6ndeland?= List-Id: virtualization@lists.linuxfoundation.org On Wed, Sep 05, 2012 at 08:15:36PM +0200, Sjur Br=E6ndeland wrote: > Hi Michael. > = > >> If the device then asks for VIRTIO_CONSOLE_F_DMA_MEM > >> when DMA is not supported, virtio will do BUG_ON() from > >> virtio_check_driver_offered_feature(). > >> > >> Is this acceptable or should we add a check in virtcons_probe() > >> and let the probing fail instead? > >> > >> E.g: > >> /* Refuse to bind if F_DMA_MEM request cannot be met */ > >> if (!VIRTIO_CONSOLE_HAS_DMA && > >> (vdev->config->get_features(vdev) & (1 << VIRTIO_CONSOLE_F_D= MA_MEM))){ > >> dev_err(&vdev->dev, > >> "DMA_MEM requested, but arch does not support DM= A\n"); > >> err =3D -EINVAL; > >> goto fail; > >> } > >> > >> Regards, > >> Sjur > > > > Failing probe would be cleaner. But there is still a problem: > > old driver will happily bind to that device and then > > fail to work, right? > = > Not just fail to work, the kernel will panic on the BUG_ON(). > Remoteproc gets the virtio configuration from firmware loaded > from user space. So this type of problem might be triggered > for other virtio drivers as well. how? > = > > virtio pci has revision id for this, but remoteproc doesn't > > seem to have anything similar. Or did I miss it? > = > No there are currently no sanity check of > virtio type and feature bits in remoteproc. > One option may be to add this... you can not fix the past. > > If not - > > we probably need to use a different > > device id, and not a feature bit. > = > But if I create a new virtio console type, remoteproc > could still call the existing virtio_console with random > bad feature bits, causing kernel panic. cirtio core checks device id - this should not happen. > Even if we fix this particular problem, the general problem > still exists: bogus virtio declarations in remoteproc's firmware > may cause BUG_ON(). which BUG_ON exactly? > (Note the fundamental difference > between visualizations and remoteproc. For remoteproc > the virtio configuration comes from binaries loaded from > user space). > = > So maybe we should look for a more generic solution, e.g. > changing virtio probe functionality so that devices with > bad feature bits will not trigger BUG_ON(), but rather refuse > to bind the driver. > = > Regards, > Sjur