linux-kernel - Re: [RESEND v2] ACPI: APEI: Skip initialization of GHES_ASSIST structures for Machine Check Architecture

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Date:   Mon, 6 Nov 2023 17:47:27 -0600
From:   Avadhut Naik <avadnaik@....com>
To:     "Luck, Tony" <tony.luck@...el.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "james.morse@....com" <james.morse@....com>,
        "bp@...en8.de" <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yazen.ghannam@....com" <yazen.ghannam@....com>,
        Avadhut Naik <avadhut.naik@....com>
Subject: Re: [RESEND v2] ACPI: APEI: Skip initialization of GHES_ASSIST
 structures for Machine Check Architecture

Hi,

On 11/6/2023 14:42, Luck, Tony wrote:
>> To support GHES_ASSIST on Machine Check Architecture (MCA) error sources,
>> a set of GHES structures is provided by the system firmware for each MCA
>> error source. Each of these sets consists of a GHES structure for each MCA
>> bank on each logical CPU, with all structures of a set sharing a common
>> Related Source ID, equal to the Source ID of one of the MCA error source
>> structures.[1] On SOCs with large core counts, this typically equates to
>> tens of thousands of GHES_ASSIST structures for MCA under
>> "/sys/bus/platform/drivers/GHES".
> 
> What combination of CONFIG options and BIOS table support results in this?
>
>From the kernel side, CONFIG_ACPI_APEI_GHES will have to be set, at the minimum.
>From the BIOS perspective, it depends on HEST Table implementation and whether
or not it supports GHES_ASSIST feature.

The actual number of GHES_ASSIST structures will depend on number of logical CPUs
in the SOC, number of MCA banks per logical CPU and the number of enabled MCA error
sources.
 
> I don't see much under "/sys/bus/platform/drivers/GHES" on my lab machine
> (Dual socket * 36 cores * HT = 144 logical CPUs).
> 
Does the BIOS on your machine support GHES_ASSIST? Can you confirm the number
of entries you actually see? 

Typically, bit 2 of the Flags field of MCA Error sources in HEST indicates
GHES_ASSIST support. Below are the results from one of my systems without and
with the patch respectively.

This system has 256 logical CPUs with 28 MCA banks (I think) per logical CPU and 2
enabled (Machine Check and Corrected Machine Check) error sources. That's a total
of (256*2*28) 14336 GHES_ASSIST structures for MCA in HEST.

[root avadnaik]# ls /sys/bus/platform/drivers/GHES/ | grep -i "ghes.*" | wc -l
14349

[root avadnaik]# ls /sys/bus/platform/drivers/GHES/ | grep -i "ghes.*" | wc -l
13

-- 
Thanks,
Avadhut Naik

> -Tony