linux-kernel - Re: [PATCH v7 9/9] ACPI: APEI: EINJ: Update the documentation for EINJv2 support

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Message-ID: <20250601102554.GAaDwqsgCODzEne7Ow@fat_crate.local>
Date: Sun, 1 Jun 2025 12:25:54 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Luck, Tony" <tony.luck@...el.com>
Cc: Zaid Alali <zaidal@...amperecomputing.com>, rafael@...nel.org,
	lenb@...nel.org, james.morse@....com, robert.moore@...el.com,
	Jonathan.Cameron@...wei.com, ira.weiny@...el.com,
	Benjamin.Cheatham@....com, dan.j.williams@...el.com, arnd@...db.de,
	Avadhut.Naik@....com, john.allen@....com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	acpica-devel@...ts.linux.dev
Subject: Re: [PATCH v7 9/9] ACPI: APEI: EINJ: Update the documentation for
 EINJv2 support

Some questions inline...

On Sat, May 31, 2025 at 03:24:14PM -0700, Luck, Tony wrote:
> EINJ V2 allows the user to perform multiple injections together.
> 
> The component_idN/component_syndromeN pairs of files direct the
> "where" and the "what" of each injection.
> 
> But the kernel needs to know how many of these pairs to use
> for an injection (to fill in a field in the structure passed
> to the BIOS).

The kernel could realloc on each write. Or we could allocate the struct to max
elems and trim it before passing it down to BIOS.

> With EINJ V2 the user might want to inject to 2 locations with
> one injection, and then just to 1 location on the next.

Right.

> Zaid Alali's version took the approach of zeroing the input
> after each injection so the user had to start from scratch
> for each injection.
> 
> I wasn't fond of that because the existing Linux EINJ interface
> saves all the paramters allowing the user to repeat the same
> injection by just runniing "echo 1 > error_inject: over and over
> (e.g. to force a soft offline by injecting multiple corrected
> errors to the same address).

I agree with you here. Linux sysfs, etc interfaces do keep their values
usually.

> User interface options:
> 
> 1) User can zero out the component_idN/component_syndromeN pairs
> that they don't need and have the kernel count how many injections
> are requested by looping to find the zero terminator.
> 
> 2) Kernel could zero all pairs after an injection to make the user
> explicitly set the list of targets each time.
> 
> 3) User provides the count vis the nr_components file (perhaps
> needs a better name?)

Yap, agree that the name is not optimal.

> 4) Something else?

See above.

User can inject into each component pairs file and the kernel can put that in
the tracking struct. So you have:

# echo 4 > component_id0
# echo A5A5A5A5 > component_syndrome0
... set other files and finish with usual
# echo 1 > error_inject

<--- here, it goes through each component pair and builds the structure to
pass down the BIOS.

And you track valid component pairs by setting the IDs to -1 or something else
invalid.

All those component IDs which have remained invalid after the error_inject
write happens, get ignored - you gather only those which are valid and inject.

And this way you can keep the old values too and gather them again and inject
again, over and over again.

Right?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette