linux-kernel - Re: [PATCH v6 06/14] iommufd/viommu: Add iommufd_viommu_get_vdev

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Message-ID: <Z7a63pqKaIpCC7MW@Asurada-Nvidia>
Date: Wed, 19 Feb 2025 21:17:18 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <corbet@....net>, <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>,
	<linux-doc@...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>,
	<ddutile@...hat.com>, <yi.l.liu@...el.com>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v6 06/14] iommufd/viommu: Add iommufd_viommu_get_vdev_id
 helper

On Tue, Feb 18, 2025 at 11:31:54AM -0400, Jason Gunthorpe wrote:
> On Fri, Jan 24, 2025 at 04:30:35PM -0800, Nicolin Chen wrote:
> > This is a reverse search v.s. iommufd_viommu_find_dev, as drivers may want
> > to convert a struct device pointer (physical) to its virtual device ID for
> > an event injection to the user space VM.
> > 
> > Again, this avoids exposing more core structures to the drivers, than the
> > iommufd_viommu alone.
> > 
> > Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >  include/linux/iommufd.h        |  9 +++++++++
> >  drivers/iommu/iommufd/driver.c | 24 ++++++++++++++++++++++++
> >  2 files changed, 33 insertions(+)
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> 
> > +	xa_lock(&viommu->vdevs);
> > +	xa_for_each(&viommu->vdevs, index, vdev) {
> > +		if (vdev->dev == dev) {
> > +			*vdev_id = (unsigned long)vdev->id;
> 
> I don't think we need this cast

The left side is ulong for xarray index, while the right side is
__aligned_u64 for uAPI. Could there be a gcc warning when somebody
builds the kernel having a BITS_PER_LONG=32?

iommufd_vdevice_alloc_ioctl() does test vdev->id against ULONG_MAX
though..

Thanks
Nicolin