Re: [PATCH RFC v1 1/2] iommu: Introduce iommu_dev_reset_prepare() and iommu_dev_reset_done()

[Robin Murphy]

On 2025-06-10 2:04 pm, Jason Gunthorpe wrote:
> On Tue, Jun 10, 2025 at 12:07:00AM -0700, Nicolin Chen wrote:
> > On Tue, Jun 10, 2025 at 12:26:07PM +0800, Baolu Lu wrote:
> > > On 6/10/25 02:45, Nicolin Chen wrote:
> > > > +	ops = dev_iommu_ops(dev);
> > >
> > > Should this be protected by group->mutext?
> >
> > Not seemingly, but should require the iommu_probe_device_lock I
> > think.
>
> group and ops are not permitted to change while a driver is attached..
>
> IIRC the FLR code in PCI doesn't always ensure that (due to the sysfs
> paths), so yeah, this looks troubled. iommu_probe_device_lock perhaps
> would fix it.

No, iommu_probe_device_lock is for protecting access to dev->iommu in 
the probe path until the device is definitively assigned to a group (or 
not). Fundamentally it defends against multiple sources triggering a 
probe of the same device in parallel - once the device *is* probed it is 
no longer relevant, and the group mutex is the right thing to protect 
all subsequent operations.

Also I'm still working towards getting rid of iommu_probe_device_lock as 
soon as I can because it's horrid... I now have most of a plan for 
making it safe to rely on device_lock() for probe, which should nicely 
solve the dev->driver races as well.

Thanks,
Robin.