[+cc regressions]
On Mon, Aug 11, 2025 at 06:44:01PM +0200, Eric Auger wrote:
> 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@xxxxxxxxxx> # pci-driver.c
> > Acked-by: Rob Herring (Arm) <robh@xxxxxxxxxx> # of/device.c
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
>
> 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.
#regzbot introduced: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
> > 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);
>
