linux-kernel - Re: RFC: IOMMU/AMD: Error Handling

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Date:	Tue, 30 Apr 2013 11:09:08 -0400
From:	Don Dutile <ddutile@...hat.com>
To:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
CC:	"Duran, Leo" <leo.duran@....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 04/30/2013 10:56 AM, Suravee Suthikulanit wrote:
> On 4/29/2013 4:42 PM, Don Dutile wrote:
>> 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.
> This sounds more like issue with the order of how things are initialized in the system.
> If so, could we separate the code which enabling of IOMMU error logging/handling and
> delay it until we are certain that systems are stable?
>
So, you are proposing we not enable fault events when IOMMU is initially configured;
use the IOMMU through boot/driver-config, hoping all is well, and if not, continue blindly,
and then enable IOMMU faults post/late-init ?

> Suravee
>

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