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

[Samiullah Khawaja <skhawaja@google.com>]

On Mon, May 18, 2026 at 02:23:17PM +0000, Pranjal Shrivastava wrote:
>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)

Oh. I will update this in next revision
>
>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 Pranjal.
>
>Thanks,
>Praan