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

[Samiullah Khawaja]

On Fri, Oct 30, 2026 at 09:26:45AM +0800, Baolu Lu wrote:
> 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>

Thanks for the review,
Sami