Re: [PATCH 04/11] iommu/amd: Use protection_domain.flags to check page table mode

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Aug 08, 2023 at 10:02:25AM +0000, Vasant Hegde wrote:
> Page table mode (v1, v2 or pt) is per domain property. Recently we have
> enhanced protection_domain.pd_mode to track per domain page table mode.
> Use that variable to check the page table mode instead of global
> 'amd_iommu_pgtable' in {map/unmap}_pages path.
> 
> Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
> ---
>  drivers/iommu/amd/iommu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

This is OK, but IMHO, it is much better to provide different ops for
the v1/v2 page table map/unmap functions since they don't really share
any code.

eg having a function pointer that does nothing other than call another
function pointer:

	struct io_pgtable_ops *ops = &domain->iop.iop.ops;
	if (ops->map_pages) {
		ret = ops->map_pages(ops, iova, paddr, pgsize,
				     pgcount, prot, gfp, mapped);
	}

Is quite inefficient these days. If you start with a map_pages_v2
domain op then you can just directly call iommu_v2_map_pages().

We did alot of work on the core side to enable this.

Jason