linux-kernel - Re: [RFC PATCH v2 16/32] iommu: Add API to preserve/unpreserve a device

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Message-ID: <CAAywjhQeL+fbyHQnmc0QKQ7OCi9pHLN5B-vu41Kxi25RLXpypA@mail.gmail.com>
Date: Thu, 4 Dec 2025 09:47:06 -0800
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: David Woodhouse <dwmw2@...radead.org>, Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, Jason Gunthorpe <jgg@...pe.ca>, iommu@...ts.linux.dev, 
	Robin Murphy <robin.murphy@....com>, Pratyush Yadav <pratyush@...nel.org>, 
	Kevin Tian <kevin.tian@...el.com>, Alex Williamson <alex@...zbot.org>, linux-kernel@...r.kernel.org, 
	Saeed Mahameed <saeedm@...dia.com>, Adithya Jayachandran <ajayachandra@...dia.com>, 
	Parav Pandit <parav@...dia.com>, Leon Romanovsky <leonro@...dia.com>, William Tu <witu@...dia.com>, 
	Vipin Sharma <vipinsh@...gle.com>, dmatlack@...gle.com, YiFei Zhu <zhuyifei@...gle.com>, 
	Chris Li <chrisl@...nel.org>, praan@...gle.com
Subject: Re: [RFC PATCH v2 16/32] iommu: Add API to preserve/unpreserve a device

On Wed, Dec 3, 2025 at 9:51 PM Baolu Lu <baolu.lu@...ux.intel.com> wrote:
>
> On 12/3/25 07:02, Samiullah Khawaja wrote:
> > iommu_preserve_device/iommu_unpreserve_device can be used to
> > preserve/unpreserve a device for liveupdate. During device preservation
> > the state of the associated IOMMU is also preserved. The device can only
> > be preseved if the attached iommu domain is preserved and the assocated
> > iommu supports preservation.
>
> If the device supports PASID, multiple domains might be attached to it.
>
> ...
>
> >
> > Signed-off-by: Samiullah Khawaja<skhawaja@...gle.com>
> > ---
> >   drivers/iommu/iommu.c      |   3 +
> >   drivers/iommu/liveupdate.c | 115 +++++++++++++++++++++++++++++++++++++
> >   include/linux/iommu-lu.h   |   2 +
> >   include/linux/iommu.h      |  18 ++++++
> >   4 files changed, 138 insertions(+)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index a70898d11959..3feb440de40a 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -382,6 +382,9 @@ static struct dev_iommu *dev_iommu_get(struct device *dev)
> >
> >       mutex_init(&param->lock);
> >       dev->iommu = param;
> > +#ifdef CONFIG_LIVEUPDATE
> > +     dev->iommu->device_ser = NULL;
> > +#endif
> >       return param;
> >   }
> >
> > diff --git a/drivers/iommu/liveupdate.c b/drivers/iommu/liveupdate.c
> > index 25a943e5e1e3..5780761a7024 100644
> > --- a/drivers/iommu/liveupdate.c
> > +++ b/drivers/iommu/liveupdate.c
> > @@ -11,6 +11,7 @@
> >   #include <linux/liveupdate.h>
> >   #include <linux/iommu-lu.h>
> >   #include <linux/iommu.h>
> > +#include <linux/pci.h>
> >   #include <linux/errno.h>
> >
> >   static void iommu_liveupdate_free_objs(u64 next, bool incoming)
> > @@ -209,3 +210,117 @@ int iommu_domain_unpreserve(struct iommu_domain *domain)
> >       return 0;
> >   }
> >   EXPORT_SYMBOL_GPL(iommu_domain_unpreserve);
> > +
> > +static int iommu_preserve_locked(struct iommu_device *iommu)
> > +{
> > +     struct iommu_lu_flb_obj *flb_obj;
> > +     struct iommu_ser *iommu_ser;
> > +     int idx, ret;
> > +
> > +     if (!iommu->ops->preserve)
> > +             return -EOPNOTSUPP;
> > +
> > +     if (iommu->outgoing_preserved_state) {
> > +             iommu->outgoing_preserved_state->obj.ref_count++;
> > +             return 0;
> > +     }
> > +
> > +     ret = liveupdate_flb_get_outgoing(&iommu_flb, (void **)&flb_obj);
> > +     if (ret)
> > +             return ret;
> > +
> > +     idx = reserve_obj_ser((struct iommu_objs_ser **)&flb_obj->iommus, MAX_IOMMU_SERS);
> > +     if (idx < 0)
> > +             return idx;
> > +
> > +     iommu_ser = &flb_obj->iommus->iommus[idx];
> > +     idx = flb_obj->ser->nr_iommus++;
> > +     iommu_ser->obj.idx = idx;
> > +     iommu_ser->obj.ref_count = 1;
> > +
> > +     ret = iommu->ops->preserve(iommu, iommu_ser);
> > +     if (ret)
> > +             iommu_ser->obj.deleted = true;
> > +
> > +     iommu->outgoing_preserved_state = iommu_ser;
> > +     return ret;
> > +}
> > +
> > +static void iommu_unpreserve_locked(struct iommu_device *iommu)
> > +{
> > +     struct iommu_ser *iommu_ser = iommu->outgoing_preserved_state;
> > +
> > +     iommu_ser->obj.ref_count--;
> > +     if (iommu_ser->obj.ref_count)
> > +             return;
> > +
> > +     iommu->outgoing_preserved_state = NULL;
> > +     iommu->ops->unpreserve(iommu, iommu_ser);
> > +     iommu_ser->obj.deleted = true;
> > +}
> > +
> > +int iommu_preserve_device(struct iommu_domain *domain, struct device *dev)
> > +{
>
> ... but this helper only cares about a single domain.

Thanks

Yes, PASID support is unimplemented in this RFC and I will be adding
PASID support when I send a non-RFC patch series. I have mentioned
this as future work in the cover letter.
Also for PASID, the PASID table also need to be preserved.

>
> > +     struct iommu_lu_flb_obj *flb_obj;
> > +     struct device_ser *device_ser;
> > +     struct dev_iommu *iommu;
> > +     struct pci_dev *pdev;
> > +     int ret, idx;
>
> Thanks,
> baolu