Re: [PATCH v2 09/16] iommu/vt-d: Restore IOMMU state and reclaimed domain ids

[Samiullah Khawaja]

On Tue, May 19, 2026 at 09:46:52PM +0000, Pranjal Shrivastava wrote:
> On Mon, Apr 27, 2026 at 05:56:26PM +0000, Samiullah Khawaja wrote:
> > During boot fetch the preserved state of IOMMU unit and if found then
> > restore the state.
> >
> > - Reuse the root_table that was preserved in the previous kernel.
> > - Reclaim the domain ids of the preserved domains for each preserved
> >   devices so these are not acquired by another domain.
> >
> > Signed-off-by: Samiullah Khawaja <skhawaja@xxxxxxxxxx>
> > ---
> >  drivers/iommu/intel/iommu.c      | 55 ++++++++++++++++++++++--------
> >  drivers/iommu/intel/iommu.h      |  7 ++++
> >  drivers/iommu/intel/liveupdate.c | 57 ++++++++++++++++++++++++++++++++
> >  3 files changed, 105 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 68fecd4e57fa..4118a0861f38 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -670,10 +670,17 @@ void dmar_fault_dump_ptes(struct intel_iommu *iommu, u16 source_id,
> >  #endif
> >
> >  /* iommu handling */
> > -static int iommu_alloc_root_entry(struct intel_iommu *iommu)
> > +static int iommu_alloc_root_entry(struct intel_iommu *iommu,
> > +				  struct iommu_hw_ser *iommu_ser)
> >  {
> >  	struct root_entry *root;
> >
> > +	if (iommu_ser) {
> > +		intel_iommu_liveupdate_restore_root_table(iommu, iommu_ser);
> > +		__iommu_flush_cache(iommu, iommu->root_entry, ROOT_SIZE);
> > +		return 0;
> > +	}
> > +
>
> Minor nit: I still believe this condition block can be moved into the
> caller? Since the called fetches iommu_ser, it can call this as a stand
> alone helper and bypass calling iommu_alloc_root_entry if (iommu_ser).

Agreed. Also as Baolu suggested the cache flush is not needed, so we can
move it out as it is self-contained. Will update this.
> >  	root = iommu_alloc_pages_node_sz(iommu->node, GFP_ATOMIC, SZ_4K);
> >  	if (!root) {
> >  		pr_err("Allocating root entry for %s failed\n",
> > @@ -992,15 +999,16 @@ static void disable_dmar_iommu(struct intel_iommu *iommu)
> >  		iommu_disable_translation(iommu);
> >  }

[snip]
> > +
> > +static int _restore_used_domain_ids(struct iommu_device_ser *ser, void *arg)
> > +{
> > +	int id = ser->domain_iommu_ser.attachment_id;
> > +	struct iommu_hw_ser *iommu_hw_ser;
> > +	struct intel_iommu *iommu = arg;
> > +
> > +	iommu_hw_ser = phys_to_virt(ser->domain_iommu_ser.iommu_phys);
>
> We should check for iommu_phys being NULL here.. I know corruptions can
> be funnier but a WARN_ON(!iommu_phys) could help catch NULL corruptions

Agreed. I will add a WARN_ON here.
> > +	if (iommu_hw_ser->type != IOMMU_INTEL)
> > +		return 0;
> > +
> > +	/* Only allocate domain ID from associated IOMMU HW unit */
> > +	if (iommu_hw_ser->intel.phys_addr != iommu->reg_phys)
> > +		return 0;
> > +
> > +	/*
> > +	 * This can fail as multiple preserved devices can share the same domain
> > +	 * ID. Since this is done during DMAR init so these failures can be
> > +	 * ignored.
> > +	 */
> > +	ida_alloc_range(&iommu->domain_ida, id, id, GFP_ATOMIC);
> > +	return 0;
> > +}
> > +
>
> Thanks,
> Praan

Sami