From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] virtio_mmio: Set DMA masks appropriately Date: Tue, 10 Jan 2017 18:07:50 +0200 Message-ID: <20170110180656-mutt-send-email-mst@kernel.org> References: <50defbbe87d75db85a9d22f914258975d661208a.1484051089.git.robin.murphy@arm.com> <20170110165221-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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: Robin Murphy Cc: will.deacon@arm.com, linux-arm-kernel@lists.infradead.org, luto@kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Tue, Jan 10, 2017 at 03:55:31PM +0000, Robin Murphy wrote: > On 10/01/17 14:54, Michael S. Tsirkin wrote: > > On Tue, Jan 10, 2017 at 12:26:01PM +0000, Robin Murphy wrote: > >> Once DMA API usage is enabled, it becomes apparent that virtio-mmio is > >> inadvertently relying on the default 32-bit DMA mask, which leads to > >> problems like rapidly exhausting SWIOTLB bounce buffers. > >> > >> Ensure that we set the appropriate 64-bit DMA mask whenever possible, > >> with the coherent mask suitably limited for the legacy vring as per > >> a0be1db4304f ("virtio_pci: Limit DMA mask to 44 bits for legacy virtio > >> devices"). > >> > >> Reported-by: Jean-Philippe Brucker > >> Fixes: b42111382f0e ("virtio_mmio: Use the DMA API if enabled") > >> Signed-off-by: Robin Murphy > >> --- > >> drivers/virtio/virtio_mmio.c | 10 ++++++++++ > >> 1 file changed, 10 insertions(+) > >> > >> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c > >> index 48bfea91dbca..b5c5d49ca598 100644 > >> --- a/drivers/virtio/virtio_mmio.c > >> +++ b/drivers/virtio/virtio_mmio.c > >> @@ -59,6 +59,7 @@ > >> #define pr_fmt(fmt) "virtio-mmio: " fmt > >> > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -497,6 +498,7 @@ static int virtio_mmio_probe(struct platform_device *pdev) > >> struct virtio_mmio_device *vm_dev; > >> struct resource *mem; > >> unsigned long magic; > >> + int rc; > >> > >> mem = platform_get_resource(pdev, IORESOURCE_MEM, 0); > >> if (!mem) > >> @@ -548,6 +550,14 @@ static int virtio_mmio_probe(struct platform_device *pdev) > >> if (vm_dev->version == 1) > >> writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE); > >> > >> + rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64)); > >> + if (rc) > >> + rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)); > >> + else if (vm_dev->version == 1) > >> + dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32 + PAGE_SHIFT)); > > > > That's a very convoluted way to do this, for version 1 you > > set coherent mask to 64 then override it. > > why not > > > > if (vm_dev->version == 1) { > > dma_set_mask > > dma_set_coherent_mask > > } else { > > dma_set_mask_and_coherent > > } > > > > if (rc) > > dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)); > > Purely because it's fewer lines of code - if you'd prefer separate > legacy vs. modern flows for clarity that's fine by me. Yes please. It's less legacy vs modern and more that I don't like line 2 undoig what line 1 did. > >> + if (rc) > >> + dev_warn(&pdev->dev, "Failed to enable 64-bit or 32-bit DMA. Trying to continue, but this might not work.\n"); > >> + > > > > is there a chance it actually still might work? > > If we're not actually using the DMA API, we may still get away with it, > otherwise it's a fairly sure bet that the subsequent dma_map/dma_alloc > calls will fail and we'll get nowhere. If I change this to be a probe > failure condition (and correspondingly in the PCI drivers too), would > you rather that be predicated on vring_use_dma_api(), or always (given > the TODO in virtio_ring.c)? > > Robin. Oh I see you are just mirroring what pci does. I think it's fine. > >> platform_set_drvdata(pdev, vm_dev); > >> > >> return register_virtio_device(&vm_dev->vdev); > >> -- > >> 2.10.2.dirty