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Tsirkin" To: Alexander Lobakin Cc: Christoph Hellwig , Ohad Ben-Cohen , Mathieu Poirier , Arnd Bergmann , Amit Shah , Greg Kroah-Hartman , Arnaud Pouliquen , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Bjorn Andersson , linux-remoteproc@vger.kernel.org, Suman Anna , virtualization@lists.linux-foundation.org Subject: Re: [PATCH virtio] virtio: virtio_console: fix DMA memory allocation for rproc serial Message-ID: <20201116080943-mutt-send-email-mst@kernel.org> References: <20201116091950.GA30524@infradead.org> <20201116071910-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Nov 16, 2020 at 01:07:28PM +0000, Alexander Lobakin wrote: > From: "Michael S. Tsirkin" > Date: Mon, 16 Nov 2020 07:25:31 -0500 > > > On Mon, Nov 16, 2020 at 09:19:50AM +0000, Christoph Hellwig wrote: > >> I just noticed this showing up in Linus' tree and I'm not happy. > > > > Are you sure? I think it's in next. > > Nope, it goes to fixes since it just fixes the regression introduced > in 5.7. Oh you are right, Greg merged it and I didn't notice because I didn't rebase my tree. > That's why it's not about any refactoring or rethinking the whole > model. > > >> This whole model of the DMA subdevices in remoteproc is simply broken. > >> > >> We really need to change the virtio code pass an expicit DMA device ( > >> similar to what e.g. the USB and RDMA code does), instead of faking up > >> devices with broken adhoc inheritance of DMA properties and magic poking > >> into device parent relationships. > > But lots of subsystems like netdev for example uses dev->parent for > DMA operations. I know that their pointers go directly to the > platform/PCI/etc. device, but still. > > The only reason behind "fake" DMA devices for rproc is to be able to > reserve DMA memory through the Device Tree exclusively for only one > virtio dev like virtio_console or virtio_rpmsg_bus. That's why > they are present, are coercing DMA caps from physical dev > representor, and why questinable dma_declare_coherent_memory() > is still here and doesn't allow to build rproc core as a module. > I agree that this is not the best model obviously, and we should take > a look at it. > > > OK but we do have a regression since 5.7 and this looks like > > a fix appropriate for e.g. stable, right? > > > >> Bjorn, I thought you were going to look into this a while ago? > >> > >> > >> On Wed, Nov 04, 2020 at 03:31:36PM +0000, Alexander Lobakin wrote: > >>> Since commit 086d08725d34 ("remoteproc: create vdev subdevice with > >>> specific dma memory pool"), every remoteproc has a DMA subdevice > >>> ("remoteprocX#vdevYbuffer") for each virtio device, which inherits > >>> DMA capabilities from the corresponding platform device. This allowed > >>> to associate different DMA pools with each vdev, and required from > >>> virtio drivers to perform DMA operations with the parent device > >>> (vdev->dev.parent) instead of grandparent (vdev->dev.parent->parent). > >>> > >>> virtio_rpmsg_bus was already changed in the same merge cycle with > >>> commit d999b622fcfb ("rpmsg: virtio: allocate buffer from parent"), > >>> but virtio_console did not. In fact, operations using the grandparent > >>> worked fine while the grandparent was the platform device, but since > >>> commit c774ad010873 ("remoteproc: Fix and restore the parenting > >>> hierarchy for vdev") this was changed, and now the grandparent device > >>> is the remoteproc device without any DMA capabilities. > >>> So, starting v5.8-rc1 the following warning is observed: > >>> > >>> [ 2.483925] ------------[ cut here ]------------ > >>> [ 2.489148] WARNING: CPU: 3 PID: 101 at kernel/dma/mapping.c:427 0x80e7eee8 > >>> [ 2.489152] Modules linked in: virtio_console(+) > >>> [ 2.503737] virtio_rpmsg_bus rpmsg_core > >>> [ 2.508903] > >>> [ 2.528898] > >>> [ 2.913043] > >>> [ 2.914907] ---[ end trace 93ac8746beab612c ]--- > >>> [ 2.920102] virtio-ports vport1p0: Error allocating inbufs > >>> > >>> kernel/dma/mapping.c:427 is: > >>> > >>> WARN_ON_ONCE(!dev->coherent_dma_mask); > >>> > >>> obviously because the grandparent now is remoteproc dev without any > >>> DMA caps: > >>> > >>> [ 3.104943] Parent: remoteproc0#vdev1buffer, grandparent: remoteproc0 > >>> > >>> Fix this the same way as it was for virtio_rpmsg_bus, using just the > >>> parent device (vdev->dev.parent, "remoteprocX#vdevYbuffer") for DMA > >>> operations. > >>> This also allows now to reserve DMA pools/buffers for rproc serial > >>> via Device Tree. > >>> > >>> Fixes: c774ad010873 ("remoteproc: Fix and restore the parenting hierarchy for vdev") > >>> Cc: stable@vger.kernel.org # 5.1+ > >>> Signed-off-by: Alexander Lobakin > >>> --- > >>> drivers/char/virtio_console.c | 8 ++++---- > >>> 1 file changed, 4 insertions(+), 4 deletions(-) > >>> > >>> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c > >>> index a2da8f768b94..1836cc56e357 100644 > >>> --- a/drivers/char/virtio_console.c > >>> +++ b/drivers/char/virtio_console.c > >>> @@ -435,12 +435,12 @@ static struct port_buffer *alloc_buf(struct virtio_device *vdev, size_t buf_size > >>> /* > >>> * Allocate DMA memory from ancestor. When a virtio > >>> * device is created by remoteproc, the DMA memory is > >>> - * associated with the grandparent device: > >>> - * vdev => rproc => platform-dev. > >>> + * associated with the parent device: > >>> + * virtioY => remoteprocX#vdevYbuffer. > >>> */ > >>> - if (!vdev->dev.parent || !vdev->dev.parent->parent) > >>> + buf->dev = vdev->dev.parent; > >>> + if (!buf->dev) > >>> goto free_buf; > >>> - buf->dev = vdev->dev.parent->parent; > >>> > >>> /* Increase device refcnt to avoid freeing it */ > >>> get_device(buf->dev); > >>> -- > >>> 2.29.2 > >>> > >>> > >> ---end quoted text--- > > Thanks, > Al