Re: [Xen-devel] ASMedia ASM1083/1085 rev3 and Xen DMA Failure

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.10.13 at 19:29, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Wed, Oct 02, 2013 at 04:43:46PM -0400, Aaron Opfer wrote:
>> First time submitting the kernel dev list, so if I have demonstrated
>> gross incompetence in some way, please cut me some slack. :)
>> 
>> I discussed with Clemens Ladisch an issue I was having that I thought
>> was related to the driver he authored for my soundcard, but on his
>> suggestion I experimented with other PCI devices and we have narrowed
>> the issue to the PCI Bridge.
>> 
>> What hints me toward DMA handling being the fault is the following
>> message I receive during kernel initialization after rebooting from an
>> Xen hypervisor into a baremetal-kernel, without a power-cycle:
>> 
>> [0.012815] dmar: DRHD: handling fault status reg 3
>> [0.012868] dmar: DMAR:[DMA Read] Request device [07:00.0] fault addr 7e00000
>> [0.012868] DMAR:[fault reason 02] Present bit in context entry is clear

That's a firmware or native Linux problem then - even during a
"warm" boot all settings a prior OS may have effected to the
hardware must be erased by the firmware (i.e. all components
have to undergo a sufficient level of resetting) for the new OS
to be permitted to make assumptions of the system coming up
in a reasonably consistent state. IOW either some assumption
made by native Linux is invalid, or the firmware doesn't make
sure a valid assumption actually holds.

Jan


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