linux-kernel - Re: [PATCH RFC v2 0/3] Add set_dev_data and unset_dev

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Message-ID: <ZEJHPb1E1/eI8V6A@Asurada-Nvidia>
Date:   Fri, 21 Apr 2023 01:20:13 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     "jgg@...dia.com" <jgg@...dia.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "will@...nel.org" <will@...nel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 0/3] Add set_dev_data and unset_dev_data support

On Fri, Apr 21, 2023 at 08:07:19AM +0000, Tian, Kevin wrote:
> External email: Use caution opening links or attachments
> 
> 
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Friday, April 21, 2023 3:56 PM
> >
> > On Fri, Apr 21, 2023 at 07:47:13AM +0000, Tian, Kevin wrote:
> >
> > > > It is in the commit message of the cover-letter though:
> > > >
> > https://github.com/nicolinc/iommufd/commit/5e17d270bfca2a5e3e7401d4b
> > > > f58ae53eb7a8a55
> > > > --------------------------------------------------------
> > > > Changelog
> > > > v2:
> > > >  * Integrated the uAPI into VFIO_DEVICE_BIND_IOMMUFD call
> > > >  * Renamed the previous set_rid_user to set_dev_data, to decouple from
> > > >    the PCI regime.
> > > > v1:
> > > >  https://lore.kernel.org/all/cover.1680762112.git.nicolinc@nvidia.com/
> > > > --------------------------------------------------------
> > > >
> > > > > Could you add some words why changing from passing the information
> > > > > in an iommufd ioctl to bind_iommufd? My gut-feeling leans toward
> > > > > the latter option...
> > > >
> > > > Yea. Jason told me to decouple it from PCI. And merge it into
> > > > a general uAPI. So I picked the BIND ioctl.
> > > >
> > >
> > > 'decouple it from PCI' is kind of covered by renaming set_rid
> > > to set_data. but I didn't get why this has to be merged with another
> > > uAPI. Once iommufd_device is created we could have separate
> > > ioctls to poke its attributes individually. What'd be broken if this
> > > is not done at BIND time?
> >
> > Oh, sorry. He didn't literally told me to merge, but commented
> > "make sense" at my proposal of reusing BIND. So, I don't think
> > adding to the BIND is a must here.
> >
> > The BIND is done in vfio_realize() where the RID (dev_data) is
> > available also. And the new uAPI in my v1 actually gets called
> > near the BIND. So, I feel we may just do it once? I am open to
> > a better idea.
> >
> 
> IMHO if this can be done within iommufd then that should be
> the choice. vfio doesn't need to know this data at all and doing
> so means vdpa or a 3rd driver also needs to implement similar
> logic in their uAPI...

Reusing the VFIO ioctl is because the device is a VFIO device.
But doing it within iommufd could save us a lot of efforts, as
you said.

So...

+/**
+ * struct iommufd_device_set_data - ioctl(IOMMU_DEVICE_SET_DATA)
+ * @size: sizeof(struct iommufd_device_set_data)
+ * @dev_id: The device to set a device data
+ * @data_uptr: User pointer of the device user data.
+ * @data_len: Length of the device user data.
+ */
+struct iommufd_device_set_data {
+	__u32 size;
+	__u32 dev_id;
+	__aligned_u64   data_uptr;
+	__u32 data_len;
+};
+#define IOMMU_DEVICE_SET_DATA _IO(IOMMUFD_TYPE, IOMMUFD_CMD_DEVICE_SET_DATA)
+
+/**
+ * struct iommufd_device_unset_data - ioctl(IOMMU_DEVICE_UNSET_DATA)
+ * @size: sizeof(struct iommufd_device_unset_data)
+ * @dev_id: The device to unset its device data
+ */
+struct iommufd_device_unset_data {
+	__u32 size;
+	__u32 dev_id;
+};
+#define IOMMU_DEVICE_UNSET_DATA _IO(IOMMUFD_TYPE, IOMMUFD_CMD_DEVICE_UNSET_DATA)

Maybe just like this?

Thanks
Nic