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Re: [PATCH 1/2] xen/ioapic: Don't use local_irq_restore() to disable irqs
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 14:40:39 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Feb 2023 13:40:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.02.2023 20:47, Andrew Cooper wrote:
> Despite its name, the irq{save,restore}() APIs are only intended to
> conditionally disable and re-enable interrupts.
Are they? Maybe nowadays they indeed are, but I couldn't spot any wording
to this effect in Linux'es Documentation/ (and I don't think we have
anywhere such could be put). Yet I'd expect such a statement to be backed
by something.
> IO-APIC's timer_irq_works() violates this intention. As it is init code,
> switch to simple irq enable/disable().
If all callers of the function obviously did have interrupts off, I might
agree. But the last of them sits _after_ local_irq_restore(), and all of
this is called from underneath smp_prepare_cpus(), i.e. after IRQs were
already enabled. I'm willing to believe that the local_irq_restore()
there really comes too early, but then, ...
> No functional change.
... in order for this to be true, that'll need fixing at the same time (or
in a prereq patch).
Jan
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