Re: RFC: IOMMU/AMD: Error Handling

[Don Dutile]

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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