Re: IOMMU+DMAR causing NMIs-s

From: Joerg Roedel
Date: Thu Jul 14 2016 - 04:31:59 EST

On Wed, Jul 13, 2016 at 05:04:08PM -0600, Alex Williamson wrote:
> With hpwdt disabled, can you reboot a few times and look for DMAR
> faults in the dmesg to see if they're all consistent, ie. device 1e.0
> doing a read from 0xb000? Is there any correlation to radeon hanging
> and one of those DMAR faults appearing in the log (you can make use of
> the iLO for a serial console so you can record more of the boot than
> what can be captured on the VGA console). Also, this should be an
> X58-based system, which reminds me of Joerg's recent commit
> a4c34ff1c029 that's intended to fix a hang on such systems. That was
> included starting in v4.7-rc4, so if this is a new issue, testing
> before and after that commit might be relevant. Thanks,

That commit fixed a hang while the IOMMU is being initialized. This hang
is different, as the IOMMU already runs. So I doubt that it fixes this
problem, but it is worth a test, of course.