linux-kernel - Re: [PATCH v3 1/1] irqchip/gic-v4.1: Disable vSGI upon (GIC CPUIF

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Date:   Wed, 17 Mar 2021 14:40:04 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        LAKML <linux-arm-kernel@...ts.infradead.org>,
        KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] irqchip/gic-v4.1: Disable vSGI upon (GIC CPUIF <
 v4.1) detection

On Wed, Mar 17, 2021 at 02:04:36PM +0000, Marc Zyngier wrote:
> Hi Lorenzo,
> 
> Wed, 17 Mar 2021 10:07:19 +0000,
> Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> > 
> > GIC CPU interfaces versions predating GIC v4.1 were not built to
> > accommodate vINTID within the vSGI range; as reported in the GIC
> > specifications (8.2 "Changes to the CPU interface"), it is
> > CONSTRAINED UNPREDICTABLE to deliver a vSGI to a PE with
> > ID_AA64PFR0_EL1.GIC < b0011.
> > 
> > Check the GIC CPUIF version by reading the SYS_ID_AA64_PFR0_EL1.
> > 
> > Disable vSGIs if a CPUIF version < 4.1 is detected to prevent using
> > vSGIs on systems where they may misbehave.
> > 
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Cc: Marc Zyngier <maz@...nel.org>
> 
> Does it need to go in as a fix? or can it just be pushed into 5.13?
> Given that there is no such HW in the wild just yet, I'm inclined to
> do the latter...

I agree with you; it is to make the driver/vgic robust against HW
misconfigurations (because that's what they are and I am not aware of
any _existing_ HW with such a misconfiguration - yet), 5.13 will
perfectly do.

Thanks a lot.

Lorenzo