linux-kernel - Re: [PATCH 0/8] arm64: Support FIQ controller registration

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Date:   Fri, 19 Feb 2021 18:10:56 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, james.morse@....com, marcan@...can.st,
        tglx@...utronix.de, will@...nel.org
Subject: Re: [PATCH 0/8] arm64: Support FIQ controller registration

Hi Mark,

On Fri, 19 Feb 2021 11:38:56 +0000,
Mark Rutland <mark.rutland@....com> wrote:
> 
> Hector's M1 support series [1] shows that some platforms have critical
> interrupts wired to FIQ, and to support these platforms we need to support
> handling FIQ exceptions. Other contemporary platforms don't use FIQ (since e.g.
> this is usually routed to EL3), and as we never expect to take an FIQ, we have
> the FIQ vector cause a panic.
> 
> Since the use of FIQ is a platform integration detail (which can differ across
> bare-metal and virtualized environments), we need be able to explicitly opt-in
> to handling FIQs while retaining the existing behaviour otherwise. This series
> adds a new set_handle_fiq() hook so that the FIQ controller can do so, and
> where no controller is registered the default handler will panic(). For
> consistency the set_handle_irq() code is made to do the same.
> 
> The first couple of patches are from Marc's irq/drop-generic_irq_multi_handler
> branch [2] on kernel.org, and clean up CONFIG_GENERIC_IRQ_MULTI_HANDLER usage.
> The next four patches move arm64 over to a local set_handle_irq()
> implementation, which is written to share code with a set_handle_fiq() function
> in the last two patches. The only functional difference here is that if an IRQ
> is somehow taken prior to set_handle_irq() the default handler will directly
> panic() rather than the vector branching to NULL.
> 
> The penultimate patch is cherry-picked from the v2 M1 series, and as per
> discussion there [3] will need a few additional fixups. I've included it for
> now as the DAIF.IF alignment is necessary for the FIQ exception handling added
> in the final patch.
> 
> The final patch adds the low-level FIQ exception handling and registration
> mechanism atop the prior rework.

Thanks for putting this together. I have an extra patch on top of this
series[1] that prevents the kernel from catching fire if a FIQ fires
whilst running a guest. Nothing urgent, we can queue it at a later time.

Thanks,

	M.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/fiq

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