From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59B87C433EF for ; Wed, 20 Apr 2022 07:48:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376386AbiDTHvV (ORCPT ); Wed, 20 Apr 2022 03:51:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344870AbiDTHvR (ORCPT ); Wed, 20 Apr 2022 03:51:17 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01918340C5; Wed, 20 Apr 2022 00:48:32 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id AFE83B81C9F; Wed, 20 Apr 2022 07:48:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2B0AC385A1; Wed, 20 Apr 2022 07:48:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1650440909; bh=k6XRQlfyfimYxWBF8lyaOnzAPgvChY3rIihTGgWCrY0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BXlGKTRkkIfgc9Qouthxl0IJUw28u32r/0tTJxjjFMDHVEltv2/4ctfYED8QMyicE 7ooiOx9xLcbdDqyuVtLCBf2hqvdqPCV5fM8zHntJrIiJnooVWGYxNUpUGTNs8O6A04 uNCPe2ft2UXpx8TPrQ8ulC7lIaqSITbTryJ/nBgs= Date: Wed, 20 Apr 2022 09:48:26 +0200 From: Greg KH To: Dan Williams Cc: Tony Luck , Hans de Goede , markgross@kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , X86 ML , "H. Peter Anvin" , Jonathan Corbet , Andy Shevchenko , "Joseph, Jithu" , "Raj, Ashok" , Steven Rostedt , Linux Kernel Mailing List , Linux Doc Mailing List , platform-driver-x86@vger.kernel.org, patches@lists.linux.dev, Ravi V Shankar Subject: Re: [PATCH v3 02/11] Documentation: In-Field Scan Message-ID: References: <20220407191347.9681-1-jithu.joseph@intel.com> <20220419163859.2228874-1-tony.luck@intel.com> <20220419163859.2228874-3-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 19, 2022 at 12:45:03PM -0700, Dan Williams wrote: > On Tue, Apr 19, 2022 at 9:48 AM Greg KH wrote: > > > > 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 > > > Signed-off-by: Tony Luck > > > --- > > > 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 > /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. > > At a minimum a separate file is needed to house the > --- > .. kernel-doc:: $source_file > :doc: $header > --- > ...statements, but ok, I'll recommend that going forward to > de-emphasize shipping content directly from Documentation/ when it can > be ingested from "DOC:" source. I had been assuming DOC: blocks in the > code were more for augmenting kernel-doc on driver internal ABIs and > not longer theory of operation documentation that is an awkward fit > for Documentation/ABI/. I don't know which is better, it's just that creating a whole new documentation file for a single tiny driver feels very odd as it will get out of date and is totally removed from the driver itself. I'd prefer that drivers be self-contained, including the documentation, as it is much more obvious what is happening with that. Spreading stuff around the tree only causes stuff to get out of sync easier. thanks, greg k-h