Re: [RFC PATCH] EDAC, ghes: Enable per-layer error reporting for ARM

[James Morse]

Hi Boris,

On 29/08/18 08:38, Borislav Petkov wrote:
> On Tue, Aug 28, 2018 at 06:09:24PM +0100, James Morse wrote:
>> Does x86 have another source of memory-topology information it needs to
>> correlate smbios with?
> 
> Bah, pinpointing the DIMM on x86 is a mess. There's no reliable way to
> say which DIMM it is in certain cases (interleaving, mirrorring, ...)
> and it is all platform-dependent. So we do the layers to dump a memory
> location (node, memory controller, ....) so that we can at least limit
> the number of DIMMs the user needs to replace/try.

Right. I'd like ghes-edac to work in the same way for both architectures.

I think this is best done by stuffing the dmi-handle in struct dimm_info during
ghes_edac_dmidecode(), then populating the struct edac_raw_error_desc layers
from the matching mci->dimms 'location'.

For EDAC_MC_LAYER_ALL_MEM this boils down to a flat index, so pointer arithmetic
on mci->dimms is an appropriate short cut.

(We should probably 'FIXME: It shouldn't be hard to also fill the DIMM labels'
at the same time so that no-one is tempted to interpret the edac:dimm-idx)


> In an ideal world, I'd like to be able to query the SPD chips on the

(oh, that can be done?)


> DIMMs and build the topology and then when an error happens to say,
> "error in DIMM <silkscreen>" where silkscreen is what is written on the
> motherboard under the DIMM socket.
> 
> But I don't see that happening any time soon...

>> For arm there is nothing else describing the memory-topology, so as long as we
>> can correlate the smbios table and ghes:cper records through the handles, we can
>> get this working for all systems.
> 
> And then make sure vendors fill in the proper info in smbios. Because that's
> also a mess on x86.

I got educated by the people who look after specifications last time I touched
this [0]. SMBIOS tables are required by Arm's 'Server Base Boot Requirements',
It lists the memory-device and physical-memory-array as required.

I will drop them a note that we will be depending on the handle, and it should
go on the list too... if its not populated on today's systems we can fall back
to !e->enable_per_layer_report as we do today.


Thanks,

James

[0] https://www.spinics.net/lists/arm-kernel/msg653133.html