Re: [PATCH v2 04/10] iommupt: Flush the CPU cache after any writes to the page table

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Sep 22, 2025 at 10:31:49AM +0800, Baolu Lu wrote:
> On 8/27/25 01:26, Jason Gunthorpe wrote:
> > @@ -585,6 +635,7 @@ static __always_inline int __do_map_single_page(struct pt_range *range,
> >   			return -EADDRINUSE;
> >   		pt_install_leaf_entry(&pts, map->oa, PAGE_SHIFT,
> >   				      &map->attrs);
> > +		/* No flush, not used when incoherent */
> >   		map->oa += PAGE_SIZE;
> >   		return 0;
> >   	}
> > @@ -811,7 +862,8 @@ int DOMAIN_NS(map_pages)(struct iommu_domain *domain, unsigned long iova,
> >   	PT_WARN_ON(map.leaf_level > range.top_level);
> >   	do {
> > -		if (single_page) {
> > +		if (single_page &&
> > +		    !pt_feature(common, PT_FEAT_DMA_INCOHERENT)) {
> >   			ret = pt_walk_range(&range, __map_single_page, &map);
> >   			if (ret != -EAGAIN)
> >   				break;
> 
> I don't follow the single_page logic here. Why is single_page exclusive
> with PT_FEAT_DMA_INCOHERENT? To my understanding, PT_FEAT_DMA_INCOHERENT
> has no relationship with how the page table is organized. Could you
> elaborate a bit?

It is this comment above:

                /* No flush, not used when incoherent */

__do_map_single_page() doesn't implement the coherency logic. As an
agressive inline I didn't want to bloat it.

Jason