Re: [PATCH v2 05/16] iommu/pages: Add APIs to preserve/unpreserve/restore iommu pages

[Pranjal Shrivastava <praan@google.com>]

On Mon, Apr 27, 2026 at 05:56:22PM +0000, Samiullah Khawaja wrote:
> IOMMU pages are allocated/freed using APIs using struct ioptdesc. For
> the proper preservation and restoration of ioptdesc add helper
> functions.
> 
> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  drivers/iommu/iommu-pages.c | 108 ++++++++++++++++++++++++++++++++++--
>  drivers/iommu/iommu-pages.h |  30 ++++++++++
>  2 files changed, 134 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/iommu-pages.c b/drivers/iommu/iommu-pages.c
> index 3bab175d8557..b1ffeb930e6d 100644
> --- a/drivers/iommu/iommu-pages.c
> +++ b/drivers/iommu/iommu-pages.c
> @@ -6,6 +6,7 @@
>  #include "iommu-pages.h"
>  #include <linux/dma-mapping.h>
>  #include <linux/gfp.h>
> +#include <linux/kexec_handover.h>
>  #include <linux/mm.h>
>  

[snip]

> +
> +/**
> + * iommu_unpreserve_pages - Unpreserve pages that were preserved in KHO
> + * @list: List of pages to unpreserve
> + */
> +void iommu_unpreserve_pages(struct iommu_pages_list *list)
> +{
> +	struct ioptdesc *iopt;
> +
> +	list_for_each_entry(iopt, &list->pages, iopt_freelist_elm)
> +		kho_unpreserve_folio(ioptdesc_folio(iopt));
> +}
> +EXPORT_SYMBOL_GPL(iommu_unpreserve_pages);
> +
> +/**
> + * iommu_restore_page - Restore a page that was preserved in KHO
> + * @phys: Physical address of a page
> + */
> +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);
> +
> +	/*
> +	 * For the restored pages incoherent is set to false as these are not
> +	 * mapped using the DMA_API. The remapping of these pages using DMA_API
> +	 * is not needed as these are not going to be written to by the new
> +	 * kernel.
> +	 */

Looks good.

> +	iopt->incoherent = false;
> +
> +	order = folio_order(folio);
> +	pgcnt = 1UL << order;
> +	iommu_folio_update_stats(folio, pgcnt);
> +}
> +EXPORT_SYMBOL_GPL(iommu_restore_page);
> +
> +/**
> + * iommu_preserve_pages - Preserve pages during kexec handover
> + * @list: List of pages to preserve
> + *
> + * Returns 0 on success, negative error on failure
> + */
> +int iommu_preserve_pages(struct iommu_pages_list *list)
> +{
> +	struct ioptdesc *iopt;
> +	int ret;
> +
> +	list_for_each_entry(iopt, &list->pages, iopt_freelist_elm) {
> +		ret = kho_preserve_folio(ioptdesc_folio(iopt));
> +		if (ret)
> +			goto err;
> +	}
> +
> +	return 0;
> +
> +err:
> +	list_for_each_entry_continue_reverse(iopt, &list->pages, iopt_freelist_elm)
> +		kho_unpreserve_folio(ioptdesc_folio(iopt));
> +

Looks good.

> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_preserve_pages);
> +#endif
> +

[snip]

> +static inline int iommu_preserve_pages(struct iommu_pages_list *list)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline void iommu_unpreserve_pages(struct iommu_pages_list *list, int count)

Nit: This is inconsistent from the signature in it's counter part in
IS_ENABLED(CONFIG_IOMMU_LIVEUPDATE)

Let's remove `int count` from the arguments to avoid broken builds.

> +{
> +}
> +
> +static inline void iommu_restore_page(u64 phys)
> +{
> +}
> +#endif
> +

With that stub argument fixed,
Reviewed-by: Pranjal Shrivastava praan@google.com

Thanks,
Praan