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

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Message-ID: <aD42uvVCULZkUq-m@zaid>
Date: Mon, 2 Jun 2025 16:41:46 -0700
From: Zaid Alali <zaidal@...amperecomputing.com>
To: "Luck, Tony" <tony.luck@...el.com>
Cc: Borislav Petkov <bp@...en8.de>, 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

On Mon, Jun 02, 2025 at 10:02:15AM -0700, Luck, Tony wrote:
> On Sun, Jun 01, 2025 at 12:25:54PM +0200, Borislav Petkov wrote:
> > 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.
> 
> The actual structure passed to BIOS is the same each time. Just the
> set_error_type_with_address::einjv2_struct::component_arr_count
> changed to indicate how many errors to inject.  In theory the
> driver could allocate and copy a correctly sized structure, but
> Zaid's code here is simpler, an this is hardly a critical path.
> 
> > > 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.
> 
> It can be dropped if we make the user zap previously supplied
> component_idN/component_syndromeN pairs that are no longer
> wanted.
> > 
> > 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.
> 
> This is just an improvement on my "option 1" (improved because all-ones
> for the component ID is going to be invalid for sure, while all zeroes
> could be a valid component).
> > 
> > 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.
> 
> Or just stop collecting on the first invalid one.
> 
> > And this way you can keep the old values too and gather them again and inject
> > again, over and over again.
> > 
> > Right?
> 
> Yup.
> 
> -Tony

Thank you Tony and Borislav, this is great feedback. I will update the patches
and send out a new revision that uses Tony's UI for the ID and syndrome.

-Zaid