Re: [PATCH v4 5/5] iommu/dma: Force swiotlb_max_mapping_size on an untrusted device

[Robin Murphy]

On 27/02/2024 3:40 pm, Christoph Hellwig wrote:
> On Wed, Feb 21, 2024 at 11:35:04AM +0000, Will Deacon wrote:
> > +static size_t iommu_dma_max_mapping_size(struct device *dev)
> > +{
> > +	if (is_swiotlb_active(dev) && dev_is_untrusted(dev))
> > +		return swiotlb_max_mapping_size(dev);
>
> Curious: do we really need both checks here?  If swiotlb is active
> for a device (for whatever reason), aren't we then always bound
> by the max size?  If not please add a comment explaining it.

Oh, good point - if we have an untrusted device but SWIOTLB isn't 
initialised for whatever reason, then it doesn't matter what 
max_mapping_size returns because iommu_dma_map_page() is going to bail 
out regardless.

Thanks,
Robin.