linux-kernel - Question about: AMD-Vi: Event logged [IO_PAGE

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Date:	Mon, 05 Jan 2015 17:25:25 +0200
From:	Raimonds Cicans <ray@...llo.lv>
To:	linux-kernel@...r.kernel.org
Subject: Question about: AMD-Vi: Event logged [IO_PAGE_FAULT ...

Hello.

After kernel upgrade (3.13 => 3.17) I started to receive following 
string in my logs:
AMD-Vi: Event logged [IO_PAGE_FAULT device=08:00.0 domain=0x001c 
address=0x0000000001355000 flags=0x0000]

I would like to deeper understand this problem, so it
would be nice if some body can fix my assumptions and
answer my questions.


Assumptions:

1) This message is generated by AMD IOMMU subsystem
      because PCIe device 08:00.0 tried to access memory
      region which was not mapped to any real memory
      (lspci show that this device is DVB-S2 receiver card
       TBS 6981)

2) Because flags are 0 and because in general receivers
     write to memory not read from memory it is memory
     write operation

3) Possible causes:
     a) memory region was never mapped
     b) device accessed memory region before it was mapped
     c) device accessed memory region after it was unmapped

3) Suspects:
      a) kernel's DMA subsystem: very unlikely
      b) kernel's IOMMU subsystem: very unlikely
      c) AMD IOMMU driver: unlikely? - i had problems with AMD IOMMU
          itself in kernels 3.14 - 3.17 (AMD-Vi: Completion-Wait loop 
timed out)
          So maybe this problem not fully fixed?
      d) Receiver's driver: likely


Questions:
1) What 'domain=0x001c' mean?
2) Where I can find definition of possible flags?
3) What kind of address is written in message?
      - physical?
      - virtual?
      - address from devices point of view?


Thank you.


Raimonds Cicans
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