Re: [PATCH v6 02/18] iommu/pages: Add APIs to preserve/unpreserve/restore iommu pages

[Baolu Lu]

On 10/25/2026 10:19 AM, Samiullah Khawaja wrote:
> IOMMU pages are allocated/freed using APIs using struct ioptdesc. For
> the proper preservation and restoration of ioptdesc add helper
> functions.
>
> Reviewed-by: Pranjal Shrivastava<praan@xxxxxxxxxx>
> Signed-off-by: Samiullah Khawaja<skhawaja@xxxxxxxxxx>
> ---
>   drivers/iommu/iommu-pages.c | 109 ++++++++++++++++++++++++++++++++++--
>   drivers/iommu/iommu-pages.h |  30 ++++++++++
>   2 files changed, 135 insertions(+), 4 deletions(-)

[...]

> +
> +/**
> + * iommu_restore_pages - Restore pages that were preserved in KHO
> + * @phys: Physical address of page to restore
> + */
> +void iommu_restore_pages(u64 phys)
> +{
> +	struct ioptdesc *iopt;
> +	struct folio *folio;
> +	unsigned long pgcnt;
> +	unsigned int order;
> +
> +	folio = kho_restore_folio(phys);
> +	if (!folio)
> +		panic("Failed to restore preserved IOMMU page %llx\n", phys);
> +
> +	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.
> +	 */
> +	iopt->incoherent = false;
> +
> +	order = folio_order(folio);
> +	pgcnt = 1UL << order;
> +	iommu_folio_update_stats(folio, pgcnt);
> +}
> +EXPORT_SYMBOL_GPL(iommu_restore_pages);

The pages were charged to the VMM's memcg in the old kernel (iommufd
maps with GFP_KERNEL_ACCOUNT), but after the live update they are no
longer charged to any memcg. I think that's fine, because the restored
tables are immutable and will be replaced by ordinary ones after boot.

This patch looks good to me,

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>