On Wed, Oct 18, 2023 at 09:27:08PM +0100, Joao Martins wrote:
> +static int iommu_v1_read_and_clear_dirty(struct io_pgtable_ops *ops,
> + unsigned long iova, size_t size,
> + unsigned long flags,
> + struct iommu_dirty_bitmap *dirty)
> +{
> + struct amd_io_pgtable *pgtable = io_pgtable_ops_to_data(ops);
> + unsigned long end = iova + size - 1;
> +
> + do {
> + unsigned long pgsize = 0;
> + u64 *ptep, pte;
> +
> + ptep = fetch_pte(pgtable, iova, &pgsize);
> + if (ptep)
> + pte = READ_ONCE(*ptep);
It is fine for now, but this is so slow for something that is such a
fast path. We are optimizing away a TLB invalidation but leaving
this???
It is a radix tree, you walk trees by retaining your position at each
level as you go (eg in a function per-level call chain or something)
then ++ is cheap. Re-searching the entire tree every time is madness.
Jason
