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

[Samiullah Khawaja]

On Thu, May 07, 2026 at 05:05:07PM +0800, Baolu Lu wrote:
> On 4/28/2026 1:56 AM, 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);
>
> The root table is already active and being used by the hardware at this
> point, correct? Since the CPU should not be modifying an active table,
> the __iommu_flush_cache() call seems unnecessary and potentially risky.
>
> Furthermore, if the iommu state has been restored, is it necessary to
> call iommu_set_root_entry()? Calling it would essentially replace an
> active, in-use root table with an identical one, which appears
> redundant.

Agreed to both points. I will remove the redundant flush here.

The set_root_entry() is done outside this function in a separate loop
after setup of all iommus, I will check whether the iommu was preserved
there and skip set_root_entry().
> > +		return 0;
> > +	}
> > +
> >  	root = iommu_alloc_pages_node_sz(iommu->node, GFP_ATOMIC, SZ_4K);
> >  	if (!root) {
> >  		pr_err("Allocating root entry for %s failed\n",
>
> Thanks,
> baolu