Re: [RFC PATCH v2 03/15] arm64: mm: change IOMMU notifier action to attach DMA ops

From: Robin Murphy
Date: Fri Jun 17 2016 - 05:27:34 EST

Hi Lorenzo,

I think this patch makes sense even independent of the rest of the series, one nit inline notwithstanding.

Marek; I'm curious as to whether this could make the workaround in 722ec35f7 obsolete as well, or are all the drivers also bound super-early in the setup you had there?

On 07/06/16 14:30, Lorenzo Pieralisi wrote:
Current bus notifier in ARM64 (__iommu_attach_notifier)
attempts to attach dma_ops to a device on BUS_NOTIFY_ADD_DEVICE
action notification.

This causes issues on ACPI based systems, where PCI devices
can be added before the IOMMUs the devices are attached to
had a chance to be probed, causing failures on attempts to
attach dma_ops in that the domain for the respective IOMMU
may not be set-up yet by the time the bus notifier is run.

Devices dma_ops do not require to be set-up till the matching
device drivers are probed. This means that instead of running
the notifier attaching dma_ops to devices (__iommu_attach_notifier)
on BUS_NOTIFY_ADD_DEVICE action, it can be run just before the
device driver is bound to the device in question (on action
BUS_NOTIFY_BIND_DRIVER) so that it is certain that its IOMMU
group and domain are set-up accordingly at the time the
notifier is triggered.

This patch changes the notifier action upon which dma_ops
are attached to devices and defer it to driver binding time,
so that IOMMU devices have a chance to be probed and to register
their bus notifiers before the dma_ops attach sequence for a
device is actually carried out.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
arch/arm64/mm/dma-mapping.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index c566ec8..79b0882 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -848,7 +848,7 @@ static int __iommu_attach_notifier(struct notifier_block *nb,
struct iommu_dma_notifier_data *master, *tmp;

- if (action != BUS_NOTIFY_ADD_DEVICE)
+ if (action != BUS_NOTIFY_BIND_DRIVER)

With this, you can also get rid of the priority setting and big fat explanatory comment in register_iommu_dma_ops_notifier().


return 0;