Message-ID: <517EE940.8010005@redhat.com>
Date:	Mon, 29 Apr 2013 17:42:24 -0400
From:	Don Dutile <ddutile@...hat.com>
To:	"Duran, Leo" <leo.duran@....com>
CC:	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RFC: IOMMU/AMD: Error Handling

On 04/29/2013 04:34 PM, Duran, Leo wrote:
> I'm wondering if resetting the IOMMU at init-time (once) would clear any BIOS induced noise.
> Leo
>
Well, depends what you mean by 'reset'....
(a) setting it up for OS use is effectively a reset, but doesn't quiesce a device
      doing dma reads of a (bios-setup) queue.  then the noisy messages begin
(b) disable the iommu, and then the dma just occurs... and bad for writes, potentially.

Similar issue is being reported & worked for kdump, where device are still
doing DMA while the system is trying to 'reset' to the kexec'd kernel, and
take a crash dump.

Solution: stop devices from doing dma... but some you _want_ enabled throughout...
           like keyboard & mouse via usb controller, so you get to pick os from
           grub...  not so for kexec...

so, again, for isolation faults.... let the hw do its job -- isolate
and throttle/silence the fault messages on a per-device, time-duration heuristic
so the system can get through boot-up where enough OS is init'd (drivers started)
to stop the temporary noise.

>> -----Original Message-----
>> From: iommu-bounces@...ts.linux-foundation.org [mailto:iommu-
>> bounces@...ts.linux-foundation.org] On Behalf Of Don Dutile
>> Sent: Monday, April 29, 2013 3:10 PM
>> To: Suthikulpanit, Suravee
>> Cc: iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
>> Subject: Re: RFC: IOMMU/AMD: Error Handling
>>
>> On 04/29/2013 03:45 PM, Suravee Suthikulanit wrote:
>>> Joerg,
>>>
>>> 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:
>>> - DEV_TAB_HADWARE_ERROR
>>> - PAGE_TAB_ERROR
>>> - COMMAND_HARDWARE_ERROR
>>> 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:
>>> - ILLEGAL_DEV_TABLE_ENTRY
>>> - IO_PAGE_FAULT
>>> - INVALDE_DEVICE_REQUEST
>>> 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,
>>> Suravee
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> iommu mailing list
>>> iommu@...ts.linux-foundation.org
>>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>
>> _______________________________________________
>> iommu mailing list
>> iommu@...ts.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
>

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