powerpc64: Ignore NVlink memory regions
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Authored by breno.leitao_gmail.com on May 18 2018, 5:41 PM.

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nwhitehorn
jhibbits

Summary

On POWER9, there are entries in /memory@ which are not standard memory
regions.

These new memory entries are related to NVLINK and the recommend way to
check if this is a memory region that the OS should use
is parsing 'linux,usable-memory' property instead of 'reg'. In machine AC922, both properties has _different_ values in fact.

If you use these NVlink memory regions as standard memory regions, you
are going to hit a machine check exception (MCE) with DAR
~0xc00003fffffd7000 and dsisr = 0x8000.

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Buildable 16675
Build 16580: arc lint + arc unit

Event Timeline

breno.leitao_gmail.com created this revision.May 18 2018, 5:41 PM

Herald added a subscriber: jhibbits. · View Herald TranscriptMay 18 2018, 5:41 PM

Harbormaster completed remote builds in B16674: Diff 42706.May 18 2018, 5:41 PM

Fixing spacing

Harbormaster completed remote builds in B16675: Diff 42707.May 18 2018, 5:44 PM

breno.leitao_gmail.com added reviewers: nwhitehorn, jhibbits.May 18 2018, 5:45 PM

This looks good, even if the deice tree situation is a bit lamentable. Two questions:

Is there a document describing this that we can reference?
If this is just part of the PowerNV platform, maybe the code belongs in platform_powernv.c instead?

Is there a document describing this that we can reference?

I was not able to find any documentation. Looking at the web, I found a patch[1] that documents it quickly in Linux, but it seems it was never accepted. I will ask internally.

If this is just part of the PowerNV platform, maybe the code belongs in platform_powernv.c instead?

At this time, yes, but I am hearing about NVLink and GPU pass-through, so, it will not surprise me if it show up in pseries.

[1] https://patchwork.kernel.org/patch/9487597/

In D15482#326710, @breno.leitao_gmail.com wrote:

Is there a document describing this that we can reference?

I was not able to find any documentation. Looking at the web, I found a patch[1] that documents it quickly in Linux, but it seems it was never accepted. I will ask internally.

Fascinating. It's how things work anyway, and the comment is good.

If this is just part of the PowerNV platform, maybe the code belongs in platform_powernv.c instead?

At this time, yes, but I am hearing about NVLink and GPU pass-through, so, it will not surprise me if it show up in pseries.

Ah, right. Let's keep it here then.

[1] https://patchwork.kernel.org/patch/9487597/

This revision is now accepted and ready to land.May 18 2018, 6:14 PM

r333825/r333826

Revision Contents
Changeset List

Path

Size

sys/

powerpc/

ofw/

ofw_machdep.c

14 lines

Diff 42707

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sys/powerpc/ofw/ofw_machdep.c

powerpc64: Ignore NVlink memory regionsClosedPublicActions