linux-kernel - Re: [PATCH v3 02/11] Documentation: In-Field Scan

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Date:   Tue, 19 Apr 2022 18:48:37 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tony Luck <tony.luck@...el.com>
Cc:     hdegoede@...hat.com, markgross@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, corbet@....net,
        andriy.shevchenko@...ux.intel.com, jithu.joseph@...el.com,
        ashok.raj@...el.com, rostedt@...dmis.org, dan.j.williams@...el.com,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, patches@...ts.linux.dev,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v3 02/11] Documentation: In-Field Scan

On Tue, Apr 19, 2022 at 09:38:50AM -0700, Tony Luck wrote:
> Add documentation for In-Field Scan (IFS). This documentation
> describes the basics of IFS, the loading IFS image, chunk
> authentication, running scan and how to check result via sysfs
> as well as tunable parameters.
> 
> The CORE_CAPABILITIES MSR enumerates whether IFS is supported.
> 
> The full  github location for distributing the IFS images is
> still being decided. So just a placeholder included for now
> in the documentation.
> 
> Future CPUs will support more than one type of test. Plan for
> that now by using a ".0" suffix on the ABI directory names.
> Additional test types will use ".1", etc.
> 
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  Documentation/x86/ifs.rst   | 101 ++++++++++++++++++++++++++++++++++++
>  Documentation/x86/index.rst |   1 +
>  2 files changed, 102 insertions(+)
>  create mode 100644 Documentation/x86/ifs.rst
> 
> diff --git a/Documentation/x86/ifs.rst b/Documentation/x86/ifs.rst
> new file mode 100644
> index 000000000000..62f3c07d433a
> --- /dev/null
> +++ b/Documentation/x86/ifs.rst
> @@ -0,0 +1,101 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=============
> +In-Field Scan
> +=============
> +
> +Introduction
> +------------
> +
> +In Field Scan (IFS) is a hardware feature to run circuit level tests on
> +a CPU core to detect problems that are not caught by parity or ECC checks.
> +Future CPUs will support more than one type of test which will show up
> +with a new platform-device instance-id, for now only .0 is exposed.
> +
> +
> +IFS Image
> +---------
> +
> +Intel provides a firmware file containing the scan tests via
> +github [#f1]_.  Similar to microcode there is a separate file for each
> +family-model-stepping.
> +
> +IFS Image Loading
> +-----------------
> +
> +The driver loads the tests into memory reserved BIOS local to each CPU
> +socket in a two step process using writes to MSRs to first load the
> +SHA hashes for the test. Then the tests themselves. Status MSRs provide
> +feedback on the success/failure of these steps. When a new test file
> +is installed it can be loaded by writing to the driver reload file::
> +
> +  # echo 1 > /sys/bus/platform/drivers/intel_ifs.0/reload
> +
> +Similar to microcode, the current version of the scan tests is stored
> +in a fixed location: /lib/firmware/intel/ifs.0/family-model-stepping.scan
> +
> +Running tests
> +-------------
> +
> +Tests are run by the driver synchronizing execution of all threads on a
> +core and then writing to the ACTIVATE_SCAN MSR on all threads. Instruction
> +execution continues when:
> +
> +1) All tests have completed.
> +2) Execution was interrupted.
> +3) A test detected a problem.
> +
> +In all cases reading the SCAN_STATUS MSR provides details on what
> +happened. The driver makes the value of this MSR visible to applications
> +via the "details" file (see below). Interrupted tests may be restarted.
> +
> +The IFS driver provides sysfs interfaces via /sys/devices/platform/intel_ifs.0/
> +to control execution:
> +
> +Test a specific core::
> +
> +  # echo <cpu#> > /sys/devices/platform/intel_ifs.0/run_test
> +
> +when HT is enabled any of the sibling cpu# can be specified to test its
> +corresponding physical core. Since the tests are per physical core, the
> +result of testing any thread is same. It is only necessary to test one
> +thread.
> +
> +For e.g. to test core corresponding to cpu5
> +
> +  # echo 5 > /sys/devices/platform/intel_ifs.0/run_test
> +
> +Results of the last test is provided in /sys::
> +
> +  $ cat /sys/devices/platform/intel_ifs.0/status
> +  pass

sysfs documentation belongs in Documentation/ABI/

And why not just include this whole thing in the driver itself and suck
the documentation out of that?  No need to have a separate file.

thanks,

greg k-h