linux-kernel - Re: [PATCH 1/2] iommufd/selftest: Use a fwnode to distinguish devices

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Date:   Tue, 28 Nov 2023 10:43:31 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, kevin.tian@...el.com, will@...nel.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iommufd/selftest: Use a fwnode to distinguish devices

On Tue, Nov 28, 2023 at 10:42:11AM +0000, Robin Murphy wrote:
> With bus ops gone, the trick of registering against a specific bus no
> longer really works, and we start getting given devices from other buses
> to probe,

Make sense

> which leads to spurious groups for devices with no IOMMU on
> arm64, 

I'm not sure I'm fully understanding what this means?

I guess that the mock driver is matching random things once it starts
being called all the time because this is missing:

 static struct iommu_device *mock_probe_device(struct device *dev)
 {
+       if (dev->bus != &iommufd_mock_bus_type)
+               return -ENODEV;
        return &mock_iommu_device;
 }

Is that sufficient to solve the problem?

> but may inadvertently steal devices from the real IOMMU on Intel,
> AMD or S390. 

AMD/Intel/S390 drivers already reject bus's they don't understand.

Intel's device_to_iommu() will fail because
for_each_active_dev_scope() will never match the mock device.

amd fails because check_device() -> get_device_sbdf_id() fails due to
no PCI and not get_acpihid_device_id().

s390 fails because !dev_is_pci(dev).

The fwspec drivers should all fail if they don't have a fwspec, and
they shouldn't for mock bus devices since it doesn't implement
dma_configure.

Jason