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Re: [PATCH v4 2/8] x86/HPET: make another channel flags update atomic
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 21 Jan 2026 18:55:49 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Wed, 21 Jan 2026 17:56:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, Nov 17, 2025 at 03:37:21PM +0100, Jan Beulich wrote:
> Unlike the setting of HPET_EVT_LEGACY in hpet_broadcast_init(), the
> setting of HPET_EVT_DISABLE in hpet_disable_legacy_broadcast() isn't init-
> only and hence can race other flag manipulation (not all of which occur
> while holding the channel's lock). While possibly any such updates would
> only ever occur when HPET_EVT_LEGACY isn't set in the first place, this
> doesn't look straightforward to prove, so better be on the safe side.
>
> Fixes: d09486dba36a ("cpuidle: Enable hpet broadcast by default")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
I also think it's quite likely that hpet_disable_legacy_broadcast() is
not possible to be used concurrently while the setting of the other
flags, that seem to happen in broadcast mode only, but better be on
the safe side.
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks, Roger.
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