linux-kernel - Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

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Message-ID: <CAAywjhS+X5o3B60hKZiioTCqT_7cYThRTz09fHmi4WnSr3ceYA@mail.gmail.com>
Date: Mon, 29 Sep 2025 10:32:22 -0700
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, 
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, iommu@...ts.linux.dev, 
	YiFei Zhu <zhuyifei@...gle.com>, Robin Murphy <robin.murphy@....com>, 
	Pratyush Yadav <pratyush@...nel.org>, Kevin Tian <kevin.tian@...el.com>, 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, Chris Li <chrisl@...nel.org>, 
	praan@...gle.com
Subject: Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

On Mon, Sep 29, 2025 at 9:00 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Sun, Sep 28, 2025 at 07:06:21PM +0000, Samiullah Khawaja wrote:
> > +static int iommufd_save_ioas(struct iommufd_ctx *ictx,
> > +                          struct iommufd_lu *iommufd_lu)
> > +{
> > +     struct iommufd_hwpt_paging *hwpt_paging;
> > +     struct iommufd_ioas *ioas = NULL;
> > +     struct iommufd_object *obj;
> > +     unsigned long index;
> > +     int rc;
> > +
> > +     /* Iterate each ioas. */
> > +     xa_for_each(&ictx->objects, index, obj) {
> > +             if (obj->type != IOMMUFD_OBJ_IOAS)
> > +                     continue;
>
> Wrong locking
>
> > +
> > +             ioas = (struct iommufd_ioas *)obj;
> > +             mutex_lock(&ioas->mutex);
> > +
> > +             /*
> > +              * TODO: Iterate over each device of this iommufd and only save
> > +              * hwpt/domain if the device is persisted.
> > +              */
> > +             list_for_each_entry(hwpt_paging, &ioas->hwpt_list, hwpt_item) {
> > +                     if (!hwpt_paging->common.domain)
> > +                             continue;
>
> I don't think this should be automatic. The user should directly
> serialize/unserialize HWPTs by ID.
Interesting. So the user should be able to serialize/unserialize HWPTs
before the Live Update PREPARE event? But what if a device was marked
for preservation but the user never serialized the attached HWPT,
would that be considered an error during LUO PREPARE or should iommufd
serialize the remaining HWPTs here?
>
> Jason