[PATCH v3 2/4] iommu/io-pgtable-arm: Add read_and_clear_dirty() support

[Jason Gunthorpe]

On Wed, May 22, 2024 at 03:37:57PM +0100, Joao Martins wrote:
 
> This is just to catch the case where IOMMUFD can call into read_and_clear()
> without dirty tracking enabled and without a bitmap structure to clear dirty
> bits -- in order to ensure a clean PTE data snapshot after start(). 

Is that broken then?

iopt_clear_dirty_data() sets the NULL:

	iommu_dirty_bitmap_init(&dirty, NULL, &gather);
		ret = ops->read_and_clear_dirty(domain, iopt_area_iova(area),
						iopt_area_length(area), 0,
						&dirty);

But AMD, for instance, does nothing:

	spin_lock_irqsave(&pdomain->lock, lflags);
	if (!pdomain->dirty_tracking && dirty->bitmap) {
		spin_unlock_irqrestore(&pdomain->lock, lflags);
		return -EINVAL;
	}
	spin_unlock_irqrestore(&pdomain->lock, lflags);

	return ops->read_and_clear_dirty(ops, iova, size, flags, dirty);

It certainly didn't clear the IOPTEs.

AFAIK the NULL should be ignored here:

static inline void iommu_dirty_bitmap_record(struct iommu_dirty_bitmap *dirty,
					     unsigned long iova,
					     unsigned long length)
{
	if (dirty->bitmap)
		iova_bitmap_set(dirty->bitmap, iova, length);

Not above. That looks like a bug. Yes?

Thanks,
Jason