Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 17 Feb 2021 14:38:27 +0000
Message-ID: <87h7mapxng.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Hector Martin <marcan@marcan.st>,
        linux-arm-kernel@lists.infradead.org,
        Rob Herring <robh@kernel.org>, Arnd Bergmann <arnd@kernel.org>,
        Olof Johansson <olof@lixom.net>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Mark Kettenis <mark.kettenis@xs4all.nl>,
        Tony Lindgren <tony@atomide.com>,
        Mohamed Mediouni <mohamed.mediouni@caramail.com>,
        Stan Skowronek <stan@corellium.com>,
        Alexander Graf <graf@amazon.com>,
        Will Deacon <will@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 09/25] arm64: entry: Map the FIQ vector to IRQ on NEEDS_FIQ platforms
In-Reply-To: <20210217114923.GB5556@C02TD0UTHF1T.local>
References: <20210215121713.57687-1-marcan@marcan.st>
        <20210215121713.57687-10-marcan@marcan.st>
        <20210217114923.GB5556@C02TD0UTHF1T.local>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1
 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Wed, 17 Feb 2021 11:49:23 +0000,
Mark Rutland <mark.rutland@arm.com> wrote:
> 
> Hi Hector,
> 
> On Mon, Feb 15, 2021 at 09:16:57PM +0900, Hector Martin wrote:
> > From: Marc Zyngier <maz@kernel.org>
> > 
> > By default, FIQ exceptions trigger a panic. On platforms that need to
> > deliver interrupts via FIQ, this gets redirected via an alternative to
> > instead handle FIQ the same way as IRQ. It is up to the irqchip handler
> > to discriminate between the two.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Hector Martin <marcan@marcan.st>
> 
> Since the use of FIQ is a platform integration detail rather than a CPU
> implementation detail (and e.g. can differ across bare-metal and VM),
> I'd prefer to always have separate registered handlers for IRQ/FIQ (also
> avoiding the need for patching). That way we can explicitly opt-in to
> FIQ when required, and avoid edge-cases where an unexpected FIQ could
> livelock an unaware IRQ handler.
> 
> Marc and I had a quick play with that, and I have a series of patches
> I've pushed to:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/fiq
> git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/fiq
> 
> ... which I'll post out shortly.

FWIW, I've just posted a more complete version of the first patch in
this series[1], which you may want to use directly (though I plan to
take it as a fix for 5.12).

Thanks,

	M.

[1] https://lore.kernel.org/r/20210217142800.2547737-1-maz@kernel.org

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