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

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Date:   Mon, 01 Oct 2018 20:22:04 -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@....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>,
        Dave Hansen <dave.hansen@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ram Pai <linuxram@...ibm.com>, Juergen Gross <jgross@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Sinan Kaya <okaya@...eaurora.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] Fix community 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 (right after efi_init) that
   will check if this system might be a UV system.

*  Patch 2 adds code into setup_arch() which disables the call to
   tsc_early_init.  This function calls the TSC adjust initialization
   functions before UV setup has checked if BIOS has set the multi-chassis
   sync flags.  Further references are in the patch.

--