Re: RFC: IOMMU/AMD: Error Handling

From: Don Dutile
Date: Mon Apr 29 2013 - 16:10:30 EST

On 04/29/2013 03:45 PM, Suravee Suthikulanit wrote:

We are in the process of implementing AMD IOMMU error handling, and I would like some comments from you and the community.

Currently, the AMD IOMMU driver only reports events from the event log in the dmesg, and does not try to handle them in case of errors. AMD IOMMU errors can be categorized as device-specific errors and IOMMU errors.

1. For IOMMU errors such as:
If the error is detected during IOMMU initialization, we could disable IOMMU and proceed. If the error occurs after IOMMU is initialized, we won't be able to recover from this, and might need to result in panic.

2. For device-specific errors such as:
We think the AMD IOMMU driver should try to isolate the device. This involves blocking device transactions at IOMMU DTE and tries to disable the device (e.g. calling the remove(struct pci_dev *pdev) interface generally provides by device drivers). This could prevents the device from continuing to fail and to risk of system instability.

disabling the device is not an option.
We've seen mis-configured ACPI tables generate storms
of invalide dte messages after iommu setup but before they are cleared up when
the OS driver is started & resets the device. The original storm is from bios-use
of IOMMU with a device.
I'd recommend creating a filter that prevents further logging from a device
for 5 mins at a time if a storm of DTE-related errors are seen.
by definition, the DMA is blocked from corrupting/changing memory, so isolation has been established;
keeping the failure log from consuming the system is the needed fix.

3. In case of posted memory write transaction, device driver might not be aware that the transaction has failed and blocked at IOMMU. If there is no HW IOMMU, I believe this is handled by PCI error handling code. If the IOMMU hardware reporth such case, could this potentially leverage the Linux IOMMU fault handling interface, iommu_set_fault_handler() and report_iommu_fault(), to communicate to device driver or PCI driver?

Wondering if you could use AER-like callback mechanism so a driver can be invoked when IOMMU error occurs,
so the device driver can quiesce or reset the device if it deems it transient.

Any feedback or comments are appreciated.

Thank you,

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