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Message-ID: <ZtnwG/Kmaf+fZFAv@nvidia.com>
Date: Thu, 5 Sep 2024 10:53:31 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <will@...nel.org>, <joro@...tes.org>,
<suravee.suthikulpanit@....com>, <robin.murphy@....com>,
<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>, <shuah@...nel.org>,
<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
<eric.auger@...hat.com>, <jean-philippe@...aro.org>, <mdf@...nel.org>,
<mshavit@...gle.com>, <shameerali.kolothum.thodi@...wei.com>,
<smostafa@...gle.com>, <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU
drivers
On Thu, Sep 05, 2024 at 01:14:15PM -0300, Jason Gunthorpe wrote:
> On Tue, Aug 27, 2024 at 09:59:47AM -0700, Nicolin Chen wrote:
> > Driver can call the iommufd_viommu_find_device() to find a device pointer
> > using its per-viommu virtual ID. The returned device must be protected by
> > the pair of iommufd_viommu_lock/unlock_vdev_id() function.
> >
> > Put these three functions into a new viommu_api file, to build it with the
> > IOMMUFD_DRIVER config.
> >
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> > drivers/iommu/iommufd/Makefile | 2 +-
> > drivers/iommu/iommufd/viommu_api.c | 39 ++++++++++++++++++++++++++++++
> > include/linux/iommufd.h | 16 ++++++++++++
> > 3 files changed, 56 insertions(+), 1 deletion(-)
> > create mode 100644 drivers/iommu/iommufd/viommu_api.c
>
> I still think this is better to just share the struct content with the
> driver, eventually we want to do this anyhow as the driver will
> want to use container_of() techniques to reach its private data.
In my mind, exposing everything to the driver is something that
we have to (for driver-managed structures) v.s. we want to...
Even in that case, a driver actually only need to know the size
of the core structure, without touching what's inside(?).
I am a bit worried that drivers would abuse the content in the
core-level structure.. Providing a set of API would encourage
them to keep the core structure intact, hopefully..
> > +/*
> > + * Find a device attached to an VIOMMU object using a virtual device ID that was
> > + * set via an IOMMUFD_CMD_VIOMMU_SET_VDEV_ID. Callers of this function must call
> > + * iommufd_viommu_lock_vdev_id() prior and iommufd_viommu_unlock_vdev_id() after
> > + *
> > + * Return device or NULL.
> > + */
> > +struct device *iommufd_viommu_find_device(struct iommufd_viommu *viommu, u64 id)
> > +{
> > + struct iommufd_vdev_id *vdev_id;
> > +
> > + lockdep_assert_held(&viommu->vdev_ids_rwsem);
> > +
> > + xa_lock(&viommu->vdev_ids);
> > + vdev_id = xa_load(&viommu->vdev_ids, (unsigned long)id);
> > + xa_unlock(&viommu->vdev_ids);
>
> No need for this lock, xa_load is rcu safe against concurrent writer
I see iommufd's device.c and main.c grab xa_lock before xa_load?
Thanks
Nicolin
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