Hi Jean,
On 3/18/20 12:40 PM, Jean-Philippe Brucker wrote:
> We don't currently support IOMMUs with a page granule larger than the
> system page size. The IOVA allocator has a BUG_ON() in this case, and
> VFIO has a WARN_ON().
>
> It might be possible to remove these obstacles if necessary. If the host
> uses 64kB pages and the guest uses 4kB, then a device driver calling
> alloc_page() followed by dma_map_page() will create a 64kB mapping for a
> 4kB physical page, allowing the endpoint to access the neighbouring 60kB
> of memory. This problem could be worked around with bounce buffers.
>
> For the moment, rather than triggering the IOVA BUG_ON() on mismatched
> page sizes, abort the virtio-iommu probe with an error message.
>
> Reported-by: Bharat Bhushan <[email protected]>
> Signed-off-by: Jean-Philippe Brucker <[email protected]>
> ---
> drivers/iommu/virtio-iommu.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 6d4e3c2a2ddb..80d5d8f621ab 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -998,6 +998,7 @@ static int viommu_probe(struct virtio_device *vdev)
> struct device *parent_dev = vdev->dev.parent;
> struct viommu_dev *viommu = NULL;
> struct device *dev = &vdev->dev;
> + unsigned long viommu_page_size;
> u64 input_start = 0;
> u64 input_end = -1UL;
> int ret;
> @@ -1028,6 +1029,14 @@ static int viommu_probe(struct virtio_device *vdev)
> goto err_free_vqs;
> }
>
> + viommu_page_size = 1UL << __ffs(viommu->pgsize_bitmap);
Given the fact we now head towards probing the device for its
page_size_mask in viommu_add_device() the check may need to happen
later, in viommu_domain_finalise() for instance?
Thanks
Eric
> + if (viommu_page_size > PAGE_SIZE) {
> + dev_err(dev, "granule 0x%lx larger than system page size
> 0x%lx\n",
> + viommu_page_size, PAGE_SIZE);
> + ret = -EINVAL;
> + goto err_free_vqs;
> + }
> +
> viommu->map_flags = VIRTIO_IOMMU_MAP_F_READ | VIRTIO_IOMMU_MAP_F_WRITE;
> viommu->last_domain = ~0U;
>
>
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