Re: [PATCH] acpi: apei: call into AER handling regardless of severity

[Sinan Kaya]

On 8/30/2017 6:16 AM, Borislav Petkov wrote:
> On Tue, Aug 29, 2017 at 06:34:49PM -0400, Sinan Kaya wrote:
>> The do_recovery function needs to be called for both uncorrectable error
>> categories. (#2 and #3 above)
> 
> Care to share why exactly that needs to happen?

Let me try below:

> 
> Because I'm reading this in pcieaer-howto.txt:
> 
> "If an error message indicates a non-fatal error, performing link reset
> at upstream is not required."
> 

Link reset is not the only recovery mechanism. In the case
of nonfatal errors, it is assumed that the endpoint CSR is still reachable. 
Error is propagated the PCIe endpoint driver. Endpoint driver does a
re-initialization, we are back in business.

> and
> 
> "If an error message indicates a fatal error, kernel will broadcast
> error_detected(dev, pci_channel_io_frozen) to all drivers within a
> hierarchy in question. Then, performing link reset at upstream is
> necessary."
> 
> Now, pci-error-recovery.txt has link reset as step 3 so I'm assuming
> recovery means link reset. And thus, non-fatal AER errors are not
> required to do recovery but fatal are.

Nope, link reset is the second approach. Endpoint recovery won't happen
if the endpoint CSRs are unreachable. We have to recover the link by
doing a link reset in this case. 

Therefore, different behavior in do_recovery function based on the
severity of the error.

> 
>> How these map to GHES error categories is out of know-how.
> 
>         case CPER_SEV_INFORMATIONAL:
>                 return GHES_SEV_NO;
>         case CPER_SEV_CORRECTED:
>                 return GHES_SEV_CORRECTED;
>         case CPER_SEV_RECOVERABLE:
>                 return GHES_SEV_RECOVERABLE;
>         case CPER_SEV_FATAL:
>                 return GHES_SEV_PANIC;
> 
> and
> 
>         case CPER_SEV_RECOVERABLE:
>                 return AER_NONFATAL;
>         case CPER_SEV_FATAL:
>                 return AER_FATAL;
>         default:
>                 return AER_CORRECTABLE;
> 

Thanks for the mapping.

> So I see GHES_SEV_RECOVERABLE -> CPER_SEV_RECOVERABLE -> AER_NONFATAL.
> 
> Which means, we've never done error recovery for AER_FATAL errors. Which
> we should've been doing in the first place! Unless...
That's not true. The GHES code is changing the severity here before posting
to the AER driver in ghes_do_proc().

	if (gdata->flags & CPER_SEC_RESET)
		aer_severity = AER_FATAL;

A PCIe error could be AER_FATAL but it is recoverable. It does not need to
crash the system.

Here is another mapping below based on my understanding.

GHES_SEV_RECOVERABLE -> CPER_SEV_RECOVERABLE -> CPER_SEC_RESET-> AER_FATAL

> 
> ... Error recovery for those fatal errors has been happening down the
> other, PCI path:
> 
> aer_isr->aer_isr_one_error->...->do_recovery()

No, AER ISR is not set up if firmware first is enabled.

> 
> Which then makes me look at this contraption in the ghes code:
> 
> config ACPI_APEI_PCIEAER
>         bool "APEI PCIe AER logging/recovering support"
>         depends on ACPI_APEI && PCIEAER
>         help
>           PCIe AER errors may be reported via APEI firmware first mode.
>           Turn on this option to enable the corresponding support.
> 
> So this says "may be" reported.
> 
> Now the question is, what kind of errors are being reported through here
> and what exactly are we expected to do about them? Print them? Or do
> more?

The behavior should match non firmware-first case ideally.

1. Print all correctable errors.
2. Go to do_recovery for all uncorrectable errors including fatal and
non-fatal. 

This is also what AER driver does in the absence of firmware first via
handle_error_source().

> 
> Hmmm.
> 


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.