[PATCH] virtio_mmio: Set DMA masks appropriately

Arnd Bergmann
2017-01-10T13:15:57Z

On Tuesday, January 10, 2017 12:26:01 PM CET Robin Murphy wrote:
> @@ -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));

You don't seem to do anything different when 64-bit DMA is unsupported.
How do you prevent the use of kernel buffers that are above the first 4G
here?

> + else if (vm_dev->version == 1)
> + dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32 + PAGE_SHIFT));

Why is this limitation only for the coherent mask?

Arnd