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Date:   Wed, 21 Apr 2021 18:56:07 +0100
Message-ID: <87tunzsers.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Sudeep Holla <sudeep.holla@arm.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Hanjun Guo <guohanjun@huawei.com>,
        dann frazier <dann.frazier@canonical.com>,
        Fu Wei <wefu@redhat.com>, Len Brown <lenb@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH 2/2] ACPI: irq: Prevent unregistering of GIC SGIs
In-Reply-To: <20210421171516.hg3ex7jqigqjqa6i@bogus>
References: <20210421164317.1718831-1-maz@kernel.org>
        <20210421164317.1718831-3-maz@kernel.org>
        <20210421171516.hg3ex7jqigqjqa6i@bogus>
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On Wed, 21 Apr 2021 18:15:16 +0100,
Sudeep Holla <sudeep.holla@arm.com> wrote:
> 
> On Wed, Apr 21, 2021 at 05:43:17PM +0100, Marc Zyngier wrote:
> > When using ACPI on arm64, which implies the GIC IRQ model, no
> > table should ever provide a GSI number in the range [0:15],
> > as these are reserved for IPIs.
> >
> > However, drivers tend to call acpi_unregister_gsi() with any
> > random GSI number provided by half baked tables, which results
> > in an exploding kernel when its IPIs have been unconfigured.
> >
> > In order to catch this, check for the silly case early, warn
> > that something is going wrong and avoid the above disaster.
> >
> 
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> 
> Just curious if this is just precaution or do we have a platform doing
> something stupid like this ?

Without this, it could be really hard to pinpoint which driver messes
with IPIs. Having this in place would have caught the GTDT bug much
earlier (several years ago actually).

The only reason I managed to track it down in a short amount of time
is that the driver actually printed an error message before the kernel
exploded while probing a completely unrelated driver. Without this
message, I'd still be scratching my head.

The WARN_ON() would definitely point at the guilty party, and keep the
kernel running.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.