Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe path

[Eric Auger <eauger@redhat.com>]

Hi Robin,

On 2/28/25 4:46 PM, Robin Murphy wrote:
> In hindsight, there were some crucial subtleties overlooked when moving
> {of,acpi}_dma_configure() to driver probe time to allow waiting for
> IOMMU drivers with -EPROBE_DEFER, and these have become an
> ever-increasing source of problems. The IOMMU API has some fundamental
> assumptions that iommu_probe_device() is called for every device added
> to the system, in the order in which they are added. Calling it in a
> random order or not at all dependent on driver binding leads to
> malformed groups, a potential lack of isolation for devices with no
> driver, and all manner of unexpected concurrency and race conditions.
> We've attempted to mitigate the latter with point-fix bodges like
> iommu_probe_device_lock, but it's a losing battle and the time has come
> to bite the bullet and address the true source of the problem instead.
> 
> The crux of the matter is that the firmware parsing actually serves two
> distinct purposes; one is identifying the IOMMU instance associated with
> a device so we can check its availability, the second is actually
> telling that instance about the relevant firmware-provided data for the
> device. However the latter also depends on the former, and at the time
> there was no good place to defer and retry that separately from the
> availability check we also wanted for client driver probe.
> 
> Nowadays, though, we have a proper notion of multiple IOMMU instances in
> the core API itself, and each one gets a chance to probe its own devices
> upon registration, so we can finally make that work as intended for
> DT/IORT/VIOT platforms too. All we need is for iommu_probe_device() to
> be able to run the iommu_fwspec machinery currently buried deep in the
> wrong end of {of,acpi}_dma_configure(). Luckily it turns out to be
> surprisingly straightforward to bootstrap this transformation by pretty
> much just calling the same path twice. At client driver probe time,
> dev->driver is obviously set; conversely at device_add(), or a
> subsequent bus_iommu_probe(), any device waiting for an IOMMU really
> should *not* have a driver already, so we can use that as a condition to
> disambiguate the two cases, and avoid recursing back into the IOMMU core
> at the wrong times.
> 
> Obviously this isn't the nicest thing, but for now it gives us a
> functional baseline to then unpick the layers in between without many
> more awkward cross-subsystem patches. There are some minor side-effects
> like dma_range_map potentially being created earlier, and some debug
> prints being repeated, but these aren't significantly detrimental. Let's
> make things work first, then deal with making them nice.
> 
> With the basic flow finally in the right order again, the next step is
> probably turning the bus->dma_configure paths inside-out, since all we
> really need from bus code is its notion of which device and input ID(s)
> to parse the common firmware properties with...
> 
> Acked-by: Bjorn Helgaas <bhelgaas@google.com> # pci-driver.c
> Acked-by: Rob Herring (Arm) <robh@kernel.org> # of/device.c
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

This patch seems to break virtio-iommu along with qemu. After applying
it we cannot see any iommu group. I don't have any specific warning in
dmesg though. Reverting bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into
the proper probe path") fixes the issue for me. Added Jerry and
jean-Philippe in the loop.

Thanks

Eric
> ---
> 
> v2:
>  - Comment bus driver changes for clarity
>  - Use dev->iommu as the now-robust replay condition
>  - Drop the device_iommu_mapped() checks in the firmware paths as they
>    weren't doing much - we can't replace probe_device_lock just yet...
>  
>  drivers/acpi/arm64/dma.c        |  5 +++++
>  drivers/acpi/scan.c             |  7 -------
>  drivers/amba/bus.c              |  3 ++-
>  drivers/base/platform.c         |  3 ++-
>  drivers/bus/fsl-mc/fsl-mc-bus.c |  3 ++-
>  drivers/cdx/cdx.c               |  3 ++-
>  drivers/iommu/iommu.c           | 24 +++++++++++++++++++++---
>  drivers/iommu/of_iommu.c        |  7 ++++++-
>  drivers/of/device.c             |  7 ++++++-
>  drivers/pci/pci-driver.c        |  3 ++-
>  10 files changed, 48 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/acpi/arm64/dma.c b/drivers/acpi/arm64/dma.c
> index 52b2abf88689..f30f138352b7 100644
> --- a/drivers/acpi/arm64/dma.c
> +++ b/drivers/acpi/arm64/dma.c
> @@ -26,6 +26,11 @@ void acpi_arch_dma_setup(struct device *dev)
>  	else
>  		end = (1ULL << 32) - 1;
>  
> +	if (dev->dma_range_map) {
> +		dev_dbg(dev, "dma_range_map already set\n");
> +		return;
> +	}
> +
>  	ret = acpi_dma_get_range(dev, &map);
>  	if (!ret && map) {
>  		end = dma_range_map_max(map);
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 9f4efa8f75a6..fb1fe9f3b1a3 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -1632,13 +1632,6 @@ static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in)
>  		err = viot_iommu_configure(dev);
>  	mutex_unlock(&iommu_probe_device_lock);
>  
> -	/*
> -	 * If we have reason to believe the IOMMU driver missed the initial
> -	 * iommu_probe_device() call for dev, replay it to get things in order.
> -	 */
> -	if (!err && dev->bus)
> -		err = iommu_probe_device(dev);
> -
>  	return err;
>  }
>  
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 8ef259b4d037..71482d639a6d 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -364,7 +364,8 @@ static int amba_dma_configure(struct device *dev)
>  		ret = acpi_dma_configure(dev, attr);
>  	}
>  
> -	if (!ret && !drv->driver_managed_dma) {
> +	/* @drv may not be valid when we're called from the IOMMU layer */
> +	if (!ret && dev->driver && !drv->driver_managed_dma) {
>  		ret = iommu_device_use_default_domain(dev);
>  		if (ret)
>  			arch_teardown_dma_ops(dev);
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 6f2a33722c52..1813cfd0c4bd 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1451,7 +1451,8 @@ static int platform_dma_configure(struct device *dev)
>  		attr = acpi_get_dma_attr(to_acpi_device_node(fwnode));
>  		ret = acpi_dma_configure(dev, attr);
>  	}
> -	if (ret || drv->driver_managed_dma)
> +	/* @drv may not be valid when we're called from the IOMMU layer */
> +	if (ret || !dev->driver || drv->driver_managed_dma)
>  		return ret;
>  
>  	ret = iommu_device_use_default_domain(dev);
> diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
> index d1f3d327ddd1..a8be8cf246fb 100644
> --- a/drivers/bus/fsl-mc/fsl-mc-bus.c
> +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
> @@ -153,7 +153,8 @@ static int fsl_mc_dma_configure(struct device *dev)
>  	else
>  		ret = acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id);
>  
> -	if (!ret && !mc_drv->driver_managed_dma) {
> +	/* @mc_drv may not be valid when we're called from the IOMMU layer */
> +	if (!ret && dev->driver && !mc_drv->driver_managed_dma) {
>  		ret = iommu_device_use_default_domain(dev);
>  		if (ret)
>  			arch_teardown_dma_ops(dev);
> diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
> index c573ed2ee71a..780fb0c4adba 100644
> --- a/drivers/cdx/cdx.c
> +++ b/drivers/cdx/cdx.c
> @@ -360,7 +360,8 @@ static int cdx_dma_configure(struct device *dev)
>  		return ret;
>  	}
>  
> -	if (!ret && !cdx_drv->driver_managed_dma) {
> +	/* @cdx_drv may not be valid when we're called from the IOMMU layer */
> +	if (!ret && dev->driver && !cdx_drv->driver_managed_dma) {
>  		ret = iommu_device_use_default_domain(dev);
>  		if (ret)
>  			arch_teardown_dma_ops(dev);
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index a3b45b84f42b..1cec7074367a 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -414,9 +414,21 @@ static int iommu_init_device(struct device *dev)
>  	if (!dev_iommu_get(dev))
>  		return -ENOMEM;
>  	/*
> -	 * For FDT-based systems and ACPI IORT/VIOT, drivers register IOMMU
> -	 * instances with non-NULL fwnodes, and client devices should have been
> -	 * identified with a fwspec by this point. Otherwise, we can currently
> +	 * For FDT-based systems and ACPI IORT/VIOT, the common firmware parsing
> +	 * is buried in the bus dma_configure path. Properly unpicking that is
> +	 * still a big job, so for now just invoke the whole thing. The device
> +	 * already having a driver bound means dma_configure has already run and
> +	 * either found no IOMMU to wait for, or we're in its replay call right
> +	 * now, so either way there's no point calling it again.
> +	 */
> +	if (!dev->driver && dev->bus->dma_configure) {
> +		mutex_unlock(&iommu_probe_device_lock);
> +		dev->bus->dma_configure(dev);
> +		mutex_lock(&iommu_probe_device_lock);
> +	}
> +	/*
> +	 * At this point, relevant devices either now have a fwspec which will
> +	 * match ops registered with a non-NULL fwnode, or we can reasonably
>  	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can
>  	 * be present, and that any of their registered instances has suitable
>  	 * ops for probing, and thus cheekily co-opt the same mechanism.
> @@ -426,6 +438,12 @@ static int iommu_init_device(struct device *dev)
>  		ret = -ENODEV;
>  		goto err_free;
>  	}
> +	/*
> +	 * And if we do now see any replay calls, they would indicate someone
> +	 * misusing the dma_configure path outside bus code.
> +	 */
> +	if (dev->driver)
> +		dev_WARN(dev, "late IOMMU probe at driver bind, something fishy here!\n");
>  
>  	if (!try_module_get(ops->owner)) {
>  		ret = -EINVAL;
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index e10a68b5ffde..6b989a62def2 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -155,7 +155,12 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
>  		dev_iommu_free(dev);
>  	mutex_unlock(&iommu_probe_device_lock);
>  
> -	if (!err && dev->bus)
> +	/*
> +	 * If we're not on the iommu_probe_device() path (as indicated by the
> +	 * initial dev->iommu) then try to simulate it. This should no longer
> +	 * happen unless of_dma_configure() is being misused outside bus code.
> +	 */
> +	if (!err && dev->bus && !dev_iommu_present)
>  		err = iommu_probe_device(dev);
>  
>  	if (err && err != -EPROBE_DEFER)
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index edf3be197265..5053e5d532cc 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -99,6 +99,11 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
>  	bool coherent, set_map = false;
>  	int ret;
>  
> +	if (dev->dma_range_map) {
> +		dev_dbg(dev, "dma_range_map already set\n");
> +		goto skip_map;
> +	}
> +
>  	if (np == dev->of_node)
>  		bus_np = __of_get_dma_parent(np);
>  	else
> @@ -119,7 +124,7 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
>  		end = dma_range_map_max(map);
>  		set_map = true;
>  	}
> -
> +skip_map:
>  	/*
>  	 * If @dev is expected to be DMA-capable then the bus code that created
>  	 * it should have initialised its dma_mask pointer by this point. For
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index f57ea36d125d..4468b7327cab 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1653,7 +1653,8 @@ static int pci_dma_configure(struct device *dev)
>  
>  	pci_put_host_bridge_device(bridge);
>  
> -	if (!ret && !driver->driver_managed_dma) {
> +	/* @driver may not be valid when we're called from the IOMMU layer */
> +	if (!ret && dev->driver && !driver->driver_managed_dma) {
>  		ret = iommu_device_use_default_domain(dev);
>  		if (ret)
>  			arch_teardown_dma_ops(dev);