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Date:   Wed, 02 Feb 2022 13:30:08 +0000
From:   Marc Zyngier <maz@kernel.org>
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        kernel-team@android.com, Steev Klimaszewski <steev@kali.org>
Subject: Re: [PATCH] irqchip/gic-v3-its: Skip HP notifier when no ITS is
 registered
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 <87pmo5o2j7.mognet@arm.com>
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On 2022-02-02 12:50, Valentin Schneider wrote:
> On 02/02/22 10:34, Marc Zyngier wrote:
>> We have some systems out there that have both LPI support and an
>> ITS, but that don't expose the ITS in their firmware tables
>> (either because it is broken or because they run under a hypervisor
>> that hides it...).
>> 
> 
> Huh :)

Yeah. Got to love these WoA machines where EL2 hides most of the
useful HW, but also can't be bothered to consistently emulate
the registers they trap (cue the bug that was causing the SMMUv2
driver to explode on store of xzr to an MMIO register). Bah.

> 
>> Is such a configuration, we still register the HP notifier to free
>> the allocated tables if needed, resulting in a warning as there is
>> no memory to free (nothing was allocated the first place).
>> 
> 
> Right, so list_empty(&its_nodes) means no ->pend_page, but still having 
> the
> HP notifier means we hit the WARN_ON(!pend_page).
> 
>> Fix it by keying the HP notifier on the presence of at least one
>> sucessfully probed ITS.
>> 
> 
> That looks fine to me.
> 
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...