linux-kernel - Re: [Xen-devel] HPET enabled in BIOS, not presented as available_clocksource -- config, kernel code, &/or BIOS?

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Message-ID: <be4448d3-7661-8653-c65f-2a023292b842@citrix.com>
Date:   Sat, 13 May 2017 20:59:37 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     pgnet.dev@...il.com, Randy Dunlap <rdunlap@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] HPET enabled in BIOS, not presented as
 available_clocksource -- config, kernel code, &/or BIOS?

On 13/05/2017 20:49, PGNet Dev wrote:
> On 5/13/17 12:38 PM, Andrew Cooper wrote:
>> What is the issue here?
>>
>> Xen owns (and may use) any HPETs in the system.  They are purposefully
>> unavailable to even dom0.
> The issue is that, when booting to Xen, hpet is not advertised as an available clocksource, AND reports the hpet boot error pointed out by Randy.
>
> Following 
>
>   https://wiki.xen.org/wiki/Xen_power_management#HPET_as_broadcast_timer_source_.28clocksource.29_.3D
>
> there's discussion there re: 'if HPET is available / not missing'.
>
> It appears to be available only booting to non-Xen.
>
> What specific indication does one look for that Xen's using available hpet?
>

Ok.  Lack of a clocksource is to be expected.

The reason why the HPETs are unavailable is that dom0 is not a position
to program them; dom0 doesn't know what Xen has set up in the IDT.

Use `xl dmesg` to get to the hypervisor dmesg log.  You should see
mention of the HPET in there if Xen has found it.

~Andrew