linux-kernel - Re: [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET hardlockup detector

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Message-ID: <alpine.DEB.2.21.1906112152430.2214@nanos.tec.linutronix.de>
Date:   Tue, 11 Jun 2019 21:54:25 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <andi.kleen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Stephane Eranian <eranian@...gle.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Clemens Ladisch <clemens@...isch.de>,
        Arnd Bergmann <arnd@...db.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET
 hardlockup detector

On Thu, 23 May 2019, Ricardo Neri wrote:

> HPET timer 2 will be used to drive the HPET-based hardlockup detector.
> Reserve such timer to ensure it cannot be used by user space programs or
> for clock events.
> 
> When looking for MSI-capable timers for clock events, skip timer 2 if
> the HPET hardlockup detector is selected.

Why? Both the changelog and the code change lack an explanation why this
timer is actually touched after it got reserved for the platform. The
reservation should make it inaccessible for other things.

Thanks,

	tglx