Re: [RFC PATCH 0/6] CPER: Add Memory Error Section 2 support

[Jonathan Cameron]

On Tue, 29 Sep 2026 09:45:59 +0200
Pierre Gondois <pierre.gondois@xxxxxxx> wrote:

> Add support for Memory Error Section 2 records.
> 
> Extend cper_mem_err_compact to hold both legacy and section-2 records.
> Add a common parser and convert the CPER, GHES, EDAC, extlog and x86 APEI
> paths to use it.
> 
> The extlog_mem_event payload layout changes with this series.
> Compatibility with existing userspace decoders still needs to be
> addressed. More specifically, the rasdaemon relies on the current
> struct cper_mem_err_compact definition.
> Either:
> A-
> this patchset should not modify struct cper_mem_err_compact and
> create a new structure to handle Memory Error Section 2 events,
> but this would ignore the similarities of Memory Error Section (1)/2
> B-
> userspace should not rely on the struct cper_mem_err_compact
> layout. extlog_mem_event trace events should instead emit data
> that relies on the actual layout of the CPER records, as defined
> in the ACPI spec.
> 
> I am looking for guidance on how to handle the above question.
> Current implementation lean toward B, but emits data in the trace
> event that maps the new/updated struct cper_mem_err_compact.

My initial thought is a no to modifying the usespace ABI.

It isn't particularly painful to just have separate handling code
for the new record.  Unfortunately the ext_log tracepoints don't
split out the fields in a fashion that would let you change
the structure.  Other RAS tracepoints do it field by field which
would have been possible to augment - even then it would have
required care to deal with field size changes.

It may be worth considering a much more 'expanded' tracepoint for
memory error section 2 to reduce similar future extension problems.
That is express ever field and don't use a compact structure at all.

Mauro, perhaps you can give input on what works better over the
long term?


Jonathan

> 
> Pierre Gondois (6):
>   ACPI: extlog: fix extlog_mem_event build issue
>   cper: add Memory Error Section 2 structures
>   cper: extend cper_mem_err_compact struct
>   cper: add helpers to handle Memory Error Section 2
>   x86/mce/apei: switch cper_sec_mem_err struct users to compact CPER
>     records
>   cper: make cper_mem_err_pack() static
> 
>  arch/x86/include/asm/mce.h     |   4 +-
>  arch/x86/kernel/acpi/apei.c    |   2 +-
>  arch/x86/kernel/cpu/mce/apei.c |   2 +-
>  drivers/acpi/acpi_extlog.c     |  23 +++-
>  drivers/acpi/apei/apei-base.c  |   2 +-
>  drivers/acpi/apei/ghes.c       |  20 +--
>  drivers/edac/ghes_edac.c       |  26 ++--
>  drivers/firmware/efi/cper.c    | 219 +++++++++++++++++++++++++++------
>  include/acpi/apei.h            |   2 +-
>  include/linux/cper.h           |  58 +++++++--
>  include/ras/ras_event.h        |   4 +-
>  11 files changed, 283 insertions(+), 79 deletions(-)
> 
> --
> 2.43.0