Re: [PATCH v3 5/8] iommu/vt-d: Implement def_domain_type iommu ops entry

Christoph Hellwig
2019-04-29T20:03:38Z

> @@ -3631,35 +3607,30 @@ static int iommu_no_mapping(struct device *dev)
> if (iommu_dummy(dev))
> return 1;
>
> - if (!iommu_identity_mapping)
> - return 0;
> -

FYI, iommu_no_mapping has been refactored in for-next:

https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git/commit/?h=x86/vt-d&id=48b2c937ea37a3bece0094b46450ed5267525289

> found = identity_mapping(dev);
> if (found) {
> + /*
> + * If the device's dma_mask is less than the system's memory
> + * size then this is not a candidate for identity mapping.
> + */
> + u64 dma_mask = *dev->dma_mask;
> +
> + if (dev->coherent_dma_mask &&
> + dev->coherent_dma_mask < dma_mask)
> + dma_mask = dev->coherent_dma_mask;
> +
> + if (dma_mask < dma_get_required_mask(dev)) {

I know this is mostly existing code moved around, but it really needs
some fixing. For one dma_get_required_mask is supposed to return the
required to not bounce mask for the given device. E.g. for a device
behind an iommu it should always just return 32-bit. If you really
want to check vs system memory please call dma_direct_get_required_mask
without the dma_ops indirection.

Second I don't even think we need to check the coherent_dma_mask,
dma_direct is pretty good at always finding memory even without
an iommu.

Third this doesn't take take the bus_dma_mask into account.

This probably should just be:

if (min(*dev->dma_mask, dev->bus_dma_mask) <
dma_direct_get_required_mask(dev)) {