linux-kernel - [PATCH 0/2] Fix TSC ADJUST breakage causing TSC failure

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Message-Id: <20181002180144.636925675@stormcage.americas.sgi.com>
Date:   Tue, 02 Oct 2018 13:01:44 -0500
From:   Mike Travis <mike.travis@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Hedi Berriche <hedi.berriche@....com>,
        Russ Anderson <russ.anderson@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Borislav Petkov <bp@...en8.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        Xiaoming Gao <gxm.linux.kernel@...il.com>,
        Rajvi Jingar <rajvi.jingar@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH 0/2] Fix TSC ADJUST breakage causing TSC failure

Fix a breakage caused by enabling early tsc initialization which bypasses
a check that disables the forcing of TSC ADJUST to 0 for chassis 0.
This is common on systems where all the chassis start up asynchronously
so which chassis should have a TSC ADJUST value of 0 is not predictable.

The solution is to add a check earlier than this early tsc init to
disable the potential of it incorrectly adjusting TSC ADJUST values that
are already correctly initialized.

*  Patch 1 adds an early callable function (after efi_init) that will
   check if this system might be a UV system.

*  Patch 2 adds code to tsc_early_init() which disables adjusting the
   TSC ADJUST value if it's a UV system.  This allows the later tsc_init
   function to test the tsc_async_resets flag that indicates the system
   chassis start up asynchronously, so which chassis should have a TSC
   ADJUST value of 0 is not predictable.  Further references are in
   the patch.

--