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Re: [PATCH 6/6] x86/idle: Fix buggy "x86/mwait-idle: enable interrupts before C1 on Xeons"
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 3 Jul 2025 11:35:09 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 03 Jul 2025 09:35:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.07.2025 16:41, Andrew Cooper wrote:
> The check of this_softirq_pending must be performed with irqs disabled, but
> this property was broken by an attempt to optimise entry/exit latency.
>
> Commit c227233ad64c in Linux (which we copied into Xen) was fixed up by
> edc8fc01f608 in Linux, which we have so far missed.
>
> Going to sleep without waking on interrupts is nonsensical outside of
> play_dead(), so overload this to select between two possible MWAITs, the
> second using the STI shadow to cover MWAIT for exactly the same reason as we
> do in safe_halt().
>
> Fixes: b17e0ec72ede ("x86/mwait-idle: enable interrupts before C1 on Xeons")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with ...
> --- a/xen/arch/x86/cpu/mwait-idle.c
> +++ b/xen/arch/x86/cpu/mwait-idle.c
> @@ -946,12 +946,8 @@ static void cf_check mwait_idle(void)
>
> update_last_cx_stat(power, cx, before);
>
> - if (cx->irq_enable_early)
> - local_irq_enable();
> -
> - mwait_idle_with_hints(cx->address, MWAIT_ECX_INTERRUPT_BREAK);
> -
> - local_irq_disable();
> + mwait_idle_with_hints(cx->address,
> + cx->irq_enable_early ? 0 :
> MWAIT_ECX_INTERRUPT_BREAK);
... indentation here switched to Linux style (to match the rest of the file).
Jan
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