linux-kernel - Re: [PATCH RFC v3 2/4] iommufd: Add IOMMUFD_CMD_DEVICE_SET_DATA and IOMMUFD_CMD_DEVICE_UNSET

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Date:   Mon, 24 Apr 2023 11:50:46 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
CC:     <jgg@...dia.com>, <kevin.tian@...el.com>, <robin.murphy@....com>,
        <eric.auger@...hat.com>, <yi.l.liu@...el.com>, <will@...nel.org>,
        <joro@...tes.org>, <shameerali.kolothum.thodi@...wei.com>,
        <jean-philippe@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v3 2/4] iommufd: Add IOMMUFD_CMD_DEVICE_SET_DATA and
 IOMMUFD_CMD_DEVICE_UNSET_DATA

Hi Baolu,

On Mon, Apr 24, 2023 at 10:44:08AM +0800, Baolu Lu wrote:

> On 4/23/23 3:40 PM, Nicolin Chen wrote:
> > Add a new pair of ioctls to allow user space to set and unset its iommu-
> > specific device data for a passthrough device that's behind the iommu.
> > 
> > On platforms with SMMUv3, this new uAPIs will be used to forward a user
> > space virtual Stream ID of a passthrough device to link to its physical
> > Stream ID and log into a lookup table, in order for the host kernel to
> > later run sanity on ATC invalidation requests from the user space, with
> > ATC_INV commands that have SID fields (virtual Stream IDs).
> > 
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >   drivers/iommu/iommufd/device.c          | 81 +++++++++++++++++++++++++
> >   drivers/iommu/iommufd/iommufd_private.h |  3 +
> >   drivers/iommu/iommufd/main.c            |  4 ++
> >   include/uapi/linux/iommufd.h            | 32 ++++++++++
> >   4 files changed, 120 insertions(+)
> > 
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index c649a3403797..9480cd36a8bd 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -136,6 +136,8 @@ void iommufd_device_destroy(struct iommufd_object *obj)
> >       struct iommufd_device *idev =
> >               container_of(obj, struct iommufd_device, obj);
> > 
> > +     if (WARN_ON(idev->has_user_data))
> > +             dev_iommu_ops(idev->dev)->unset_dev_user_data(idev->dev);
> 
> Do you really need this WARN_ON()? The user space application can easily
> trigger this kernel WARN() by setting the user data and forgetting to
> unset it.

I can drop that, since it's a user triggerable one.

Thanks
Nic