Messages in this thread Patch in this message | | | Subject | Re: arm64 iommu groups issue | From | Robin Murphy <> | Date | Thu, 13 Feb 2020 19:40:42 +0000 |
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On 13/02/2020 3:49 pm, John Garry wrote: >>> >>> The underlying issue is that, for historical reasons, OF/IORT-based >>> IOMMU drivers have ended up with group allocation being tied to endpoint >>> driver probing via the dma_configure() mechanism (long story short, >>> driver probe is the only thing which can be delayed in order to wait for >>> a specific IOMMU instance to be ready).However, in the meantime, the >>> IOMMU API internals have evolved sufficiently that I think there's a way >>> to really put things right - I have the spark of an idea which I'll try >>> to sketch out ASAP... >>> >> >> OK, great. > > Hi Robin, > > I was wondering if you have had a chance to consider this problem again?
Yeah, sorry, more things came up such that it still hasn't been P yet ;)
Lorenzo and I did get as far as discussing it a bit more and writing up a ticket, so it's formally on our internal radar now, at least.
> One simple idea could be to introduce a device link between the endpoint > device and its parent bridge to ensure that they probe in order, as > expected in pci_device_group(): > > Subject: [PATCH] PCI: Add device link to ensure endpoint device driver > probes after bridge > > It is required to ensure that a device driver for an endpoint will probe > after the parent port driver, so add a device link for this. > > --- > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 512cb4312ddd..4b832ad25b20 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -2383,6 +2383,7 @@ static void pci_set_msi_domain(struct pci_dev *dev) > void pci_device_add(struct pci_dev *dev, struct pci_bus *bus) > { > int ret; > + struct device *parent; > > pci_configure_device(dev); > > @@ -2420,6 +2421,10 @@ void pci_device_add(struct pci_dev *dev, struct > pci_bus *bus) > /* Set up MSI IRQ domain */ > pci_set_msi_domain(dev); > > + parent = dev->dev.parent; > + if (parent && parent->bus == &pci_bus_type) > + device_link_add(&dev->dev, parent, DL_FLAG_AUTOPROBE_CONSUMER); > + > /* Notifier could use PCI capabilities */ > dev->match_driver = false; > ret = device_add(&dev->dev); > -- > > This would work, but the problem is that if the port driver fails in > probing - and not just for -EPROBE_DEFER - then the child device will > never probe. This very thing happens on my dev board. However we could > expand the device links API to cover this sort of scenario.
Yes, that's an undesirable issue, but in fact I think it's mostly indicative that involving drivers in something which is designed to happen at a level below drivers is still fundamentally wrong and doomed to be fragile at best.
Another thought that crosses my mind is that when pci_device_group() walks up to the point of ACS isolation and doesn't find an existing group, it can still infer that everything it walked past *should* be put in the same group it's then eventually going to return. Unfortunately I can't see an obvious way for it to act on that knowledge, though, since recursive iommu_probe_device() is unlikely to end well.
> As for alternatives, it looks pretty difficult to me to disassociate the > group allocation from the dma_configure path.
Indeed it's non-trivial, but it really does need cleaning up at some point.
Having just had yet another spark, does something like the untested super-hack below work at all? I doubt it's a viable direction to take in itself, but it could be food for thought if it at least proves the concept.
Robin.
----->8----- diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index aa3ac2a03807..554cde76c766 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c @@ -3841,20 +3841,20 @@ static int arm_smmu_set_bus_ops(struct iommu_ops *ops) int err;
#ifdef CONFIG_PCI - if (pci_bus_type.iommu_ops != ops) { + if (1) { err = bus_set_iommu(&pci_bus_type, ops); if (err) return err; } #endif #ifdef CONFIG_ARM_AMBA - if (amba_bustype.iommu_ops != ops) { + if (1) { err = bus_set_iommu(&amba_bustype, ops); if (err) goto err_reset_pci_ops; } #endif - if (platform_bus_type.iommu_ops != ops) { + if (1) { err = bus_set_iommu(&platform_bus_type, ops); if (err) goto err_reset_amba_ops; diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 660eea8d1d2f..b81ae2b4d4fb 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -1542,6 +1542,14 @@ static int iommu_bus_init(struct bus_type *bus, const struct iommu_ops *ops) return err; }
+static int iommu_bus_replay(struct device *dev, void *data) +{ + if (dev->iommu_group) + return 0; + + return add_iommu_group(dev, data); +} + /** * bus_set_iommu - set iommu-callbacks for the bus * @bus: bus. @@ -1564,6 +1572,9 @@ int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops) return 0; }
+ if (bus->iommu_ops == ops) + return bus_for_each_dev(bus, NULL, NULL, iommu_bus_replay); + if (bus->iommu_ops != NULL) return -EBUSY;
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