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

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Message-ID: <20250220161948.GD50639@nvidia.com>
Date: Thu, 20 Feb 2025 12:19:48 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...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 Wed, Feb 19, 2025 at 09:17:18PM -0800, Nicolin Chen wrote:
> 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?

No. The kernel is full of these implicit casts

Jason