linux-kernel - Re: [PATCH v2 0/7] irqchip/apple-aic: Add support for AICv2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87r17s2ifv.wl-maz@kernel.org>
Date:   Thu, 24 Feb 2022 19:06:12 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Hector Martin <marcan@...can.st>,
        Mark Rutland <mark.rutland@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 0/7] irqchip/apple-aic: Add support for AICv2

On Thu, 24 Feb 2022 18:26:41 +0000,
Mark Rutland <mark.rutland@....com> wrote:
> 
> On Thu, Feb 24, 2022 at 10:07:34PM +0900, Hector Martin wrote:
> > Hi folks,
> 
> Hi Hector,
> 
> > In the t6000/t6001 (M1 Pro / Max) SoCs, Apple introduced a new version
> > of their interrupt controller. This is a significant departure from
> > AICv1 and seems designed to better scale to larger chips. This series
> > adds support for it to the existing AIC driver.
> > 
> > Gone are CPU affinities; instead there seems to be some kind of
> > "automagic" dispatch to willing CPU cores, and cores can also opt-out
> > via an IMP-DEF sysreg (!). Right now the bootloader just sets up all
> > cores to accept IRQs, and we ignore all this and let the magic
> > algorithm pick a CPU to accept the IRQ.
> 
> Maybe that's ok for the set of peripherals attached, but in general that
> violates existing expectations regarding affinity, and I fear there'll
> be some subtle brokenness resulting from this automatic target
> selection.
> 
> For example, in the perf events subsystem there are PMU drivers (even
> those for "uncore" or "system" devices which are shared by many/all
> CPUs) which rely on a combination of interrupt affinity and local IRQ
> masking (without any other locking) to provide exclusion between a PMU's
> IRQ handler and any other management operations for that PMU (which are
> all handled from the same CPU).

It will definitely break anything that relies on managed interrupts,
where the kernel expects to allocate interrupts that have a strict
affinity. Drivers using this feature can legitimately expect that they
can keep their state in per-CPU pointers, and that obviously breaks.

This may affect any PCIe device with more than a couple of queues.
Maybe users of this HW do not care (yet), but we'll have to find a way
to tell drivers of the limitation.

	M.

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