Re: Regression from dcadfd7f7c74ef9ee415e072a19bdf6c085159eb

[Takashi Sakamoto]

Hi Mario,

On Tue, Nov 07, 2023 at 03:27:08PM -0600, Mario Limonciello wrote:
> +linux-pci / Bjorn
> On 11/7/2023 06:17, Takashi Sakamoto wrote:
> > Hi Mario,
> > 
> > Thanks for the report.
> > 
> > I apologize for the inconvenience you and your reporter facing, however
> > I can not avoid to say that the problem appears to be specific to the AMD
> > Ryzen machines.
> 
> Unfortunately I don't have this 1394 hardware myself.  I was just looking at
> another completely unrelated issue on Bugzilla and noticed the report come
> up in my search and wanted to ensure it's on your radar already as the
> author as it's lingered a while.

It is your misfortune to face this kind of machine trouble.

In the report[1], Matthias Schrumpf and Mark Broadworth noted to use AMD
Ryzen 7 5800X on B550/X570 chipsets, and insert VT6307 in their PCIe bus.
I guess that the device attends PCI bridge (ASM1083) since VT6307 has PCI
interface only.

We can see MCE error in another report[2]. Unfortunately, the reporter,
Ian Donnelly, have less suspiction about machine architecture, and never
provides hardware information. But I believe that it comes from AMD Ryzen
machine. I transcribe the error here:

```
[    0.860834] mce: [Hardware Error]: Machine check events logged
[    0.860834] microcode: CPU20: patch_level=0x0a201025
[    0.860835] microcode: CPU21: patch_level=0x0a201025
[    0.860836] microcode: CPU23: patch_level=0x0a201025
[    0.860836] microcode: CPU22: patch_level=0x0a201025
[    0.860837] mce: [Hardware Error]: CPU 17: Machine Check: 0 Bank 0: bc00080001010135
[    0.860845] fbcon: Taking over console
[    0.860847] mce: [Hardware Error]: TSC 0 ADDR fca000f0 MISC d012000000000000 IPID 1000b000000000 
[    0.860854] mce: [Hardware Error]: PROCESSOR 2:a20f10 TIME 1696955537 SOCKET 0 APIC b microcode a201025
[    0.860860] microcode: CPU0: patch_level=0x0a201025
[    0.861676] microcode: Microcode Update Driver: v2.2.
```

Additionally, as I note in the PR[3], I observed cache-coherence failure
over memory dedicated for DMA transmission. The mapping is created by
`dmam_alloc_coherent()` and no need to have extra care such as streaming
API. However, the combination of ASM1083 and VT6307 provides me bogus
values from the memory in AMD Ryzen machine, and I can see no issue in
Intel machines.

Essentially, the host system reboots when firewire-ohci module in guest
system probes the PCI device for 1394 OHCI hardware provided by PCI
pass-though[4].

> > I've already received the similar report[1], and have been
> > investigating it in the last few weeks, then got the insight. Please take
> > a look at my short report about it in PR to Linus for 6.7-rc1:
> > https://lore.kernel.org/lkml/20231105144852.GA165906@workstation.local/
> > 
> > I can confirm that I have been abe to reproduce the problem on AMD Ryzen
> > machine. However, it's important to note that I have not observed the
> > problem on the following systems:
> 
> Any chance you (or anyone with the issue) has a serial output available?
> I think it would be really good to look at the circumstances surrounding the
> reboot.
>
> > 
> > * Intel machine (Sandy Bridge and Skylake generations)
> > * AMD machines predating Ryzen (Sempron 145)
> > * Machines using different 1394 OHCI hardware from other vendors such as
> >    TI
> > * VIA VT6307 connected directly to PCI slot (i.e. without the issued
> >    PCIe/PCI bridge)
> > 
> > Currently, I have not been able to obtain any useful debug output from
> > the Linux system or any hardware error reports when the system reboots.
> > It seems that the system reboots spontaneously. My assumption at this
> > point is that AMD Ryzen machines detect a specific hardware error
> > triggered by Ryzen machine quirk related to the combination of the Asmedia
> > ASM1083/1085 and VIA VT6306/6307/6308, leading to power reset.
> > 
> 
> Recent kernels have enabled PCI AER.  Could that be factoring in perhaps?

I ordered equipments for the workflow, and waiting for shipping, since
my motherboard has no interface for serial output.

(However, I predict that we can no helpful output via the interface.)

> > I genuinely appreciate your assistance in debugging this elusive
> > hardware issue. If any workaround specific to AMD Ryzen machine quirk is
> > required in PCI driver for 1394 OHCI hardware, I'm willing to apply it.
> > However, it is preferable to figure out the reboot mechanism at first,
> > I think.
> 
> Does the BIOS on these machines enable a watchdog timer?  If so, I'd suggest
> disabling that for a starting point.
 
For consumer use, the machine has no such function, I think. For
your information, this is the machine information I used:

* Ryzen 5 2400G
* Gigabyte Technology Co., Ltd. AX370-Gaming 5/AX370-Gaming 5
    * BIOS F51h 02/09/2023

> How about if you compile as a module and then modprobe.blacklist the module
> on kernel command line and load it later.  Can you trigger the fault/reboot
> this way?  If so, it at least rules out some conditions that happen during a
> race at boot.

Nowadays FireWire software stack is optional in the most of
distributions. I can encounter the same issue at deferred probing enough
after booting up, even if the load of system is very low.

> Looking more closely at the change, I would guess the fault is specifically
> in get_cycle_time().  I can see that the VIA devices do set
> QUIRK_CYCLE_TIMER which will cause additional reads.

I've already tested with the driver compiled without these codes, but the
system reboots again.

> Another guesses worth looking at is to see if iommu=pt or amd_iommu=off
> help.
> 
> If either of those help it could point at being a problem with
> get_cycle_time() and IOMMU.  The older systems you mentioned working
> probably didn't enable IOMMU by default but most AMD Ryzen systems do.

I already suspect platform IOMMU and kernel implementation, however it
is helpless to disable AMD SVM and IOMMU in BIOS settings. Of course, it
is helpless as well to provide any options to iommu in kernel command line.

If I had any opportunity to access to AMD machines for enterprise-grade
usage somehow, I would have done it. However, I am a private-time
contributor and what I can access to is the ones for consumer use
without any hardware support for RAS reporting.


[1] https://bugzilla.kernel.org/show_bug.cgi?id=217993
[2] https://bugzilla.kernel.org/show_bug.cgi?id=217994
[3] https://lore.kernel.org/lkml/20231105144852.GA165906@workstation.local/
[4] https://lore.kernel.org/lkml/20231016155657.GA7904@workstation.local/

Thanks

Takashi Sakamoto