Re: [Xen-devel] [RFC XEN PATCH v3 08/11] xen: arm: vgic: don't fail if IRQ is already connected

From: Julien Grall <julien@xen.org>
To: Stewart Hildebrand <stewart.hildebrand@dornerworks.com>,
	xen-devel@lists.xenproject.org
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [RFC XEN PATCH v3 08/11] xen: arm: vgic: don't fail if IRQ is already connected
Date: Tue, 3 Dec 2019 14:24:19 +0000	[thread overview]
Message-ID: <a231c763-2ca0-c1f1-89c5-fd94771e8736@xen.org> (raw)
In-Reply-To: <20191115201037.44982-4-stewart.hildebrand@dornerworks.com>

Hi,

On 15/11/2019 20:10, Stewart Hildebrand wrote:
> There are some IRQs that happen to have multiple "interrupts = < ... >;"
> properties with the same IRQ in the device tree. For example:
> 
> interrupts = <0 123 4>,
>               <0 123 4>,
>               <0 123 4>,
>               <0 123 4>,
>               <0 123 4>;
> 
> In this case it seems that we are invoking vgic_connect_hw_irq multiple
> times for the same IRQ.
> 
> Rework the checks to allow booting in this scenario.
> 
> I have not seen any cases where the pre-existing p->desc is any different from
> the new desc, so BUG() out if they're different for now.
> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@dornerworks.com>
> 
> ---
> v3: new patch
> 
> I tested on Xilinx Zynq UltraScale+ with the old vGIC. I have not fully
> tested with CONFIG_NEW_VGIC. This hack only became necessary after
> introducing the PPI series, and I'm not entirely sure what the reason
> is for that.
> 
> I'm also unsure if BUG()ing out is the right thing to do in case of
> desc != p->desc, or what conditions would even trigger this? Is this
> function exposed to guests?

This can happen with PPIs as the desc is per-CPU. If you migrate the 
vCPU to another pCPU, you will likely hit the BUG() below if the guest 
disabled the interrupt.

But I don't think we should call vgic_connect_hw_irq() multiples time on 
the same IRQ. The upper layer should take care of such issue (such as 
setup_guest_irq()).

Cheers,

-- 
Julien Grall

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