Re: [PATCH 04/14] iommu/pages: Add APIs to preserve/unpreserve/restore iommu pages

[Pranjal Shrivastava <praan@google.com>]

On Tue, Mar 17, 2026 at 01:59:03PM -0700, Vipin Sharma wrote:
> On Tue, Feb 03, 2026 at 10:09:38PM +0000, Samiullah Khawaja wrote:
> > +

[------- snip >8 --------]

> > +EXPORT_SYMBOL_GPL(iommu_unpreserve_pages);
> > +
> > +void iommu_restore_page(u64 phys)
> > +{
> > +	struct ioptdesc *iopt;
> > +	struct folio *folio;
> > +	unsigned long pgcnt;
> > +	unsigned int order;
> > +
> > +	folio = kho_restore_folio(phys);
> > +	BUG_ON(!folio);
> > +
> > +	iopt = folio_ioptdesc(folio);
> > +
> > +	order = folio_order(folio);
> > +	pgcnt = 1UL << order;
> > +	mod_node_page_state(folio_pgdat(folio), NR_IOMMU_PAGES, pgcnt);
> > +	lruvec_stat_mod_folio(folio, NR_SECONDARY_PAGETABLE, pgcnt);
> 
> Above two functions are also used in other two places in this file, lets
> create a common function for these two operations.
> 

I was thinking about this, out of the 2 other places one is 
`__iommu_free_desc` where we are supposed to subtract pgcnt.. but I
think we can follow the -pgcnt pattern we have currently and add a
helper `iommu_folio_update_stats(folio, pgcnt)` where we can pass -pgcnt
to subtract nr_pages? Something like:

+static inline void iommu_folio_update_stats(struct folio *folio, long nr_pages)
+{
+	mod_node_page_state(folio_pgdat(folio), NR_IOMMU_PAGES, nr_pages);
+	lruvec_stat_mod_folio(folio, NR_SECONDARY_PAGETABLE, nr_pages);
+}

@@ -86,8 +91,7 @@ static void __iommu_free_desc(struct ioptdesc *iopt)
 	if (IOMMU_PAGES_USE_DMA_API)
 		WARN_ON_ONCE(iopt->incoherent);

-	mod_node_page_state(folio_pgdat(folio), NR_IOMMU_PAGES, -pgcnt);
-	lruvec_stat_mod_folio(folio, NR_SECONDARY_PAGETABLE, -pgcnt);
+	iommu_folio_update_stats(folio, -(long)pgcnt);
 	folio_put(folio);
 }

But I'm unsure if passing -(long)pgcnt is a good idea?

> > +}
> > +EXPORT_SYMBOL_GPL(iommu_restore_page);
> > +

Thanks,
Praan