Re: [Xen-devel] [PATCH for-4.12] xen/arm: irq: End cleanly spurious interrupt

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 28 Jan 2019, Julien Grall wrote:
> no_irq_type handlers are used when an IRQ does not have action attached.
> This is useful to detect misconfiguration between the interrupt
> controller and the software.
> 
> Currently, all the handlers will do nothing on spurious interrupt. This
> means if such interrupt is received, the priority of the interrupt will
> not be dropped and the processor will lose the ability to receive any
> interrupt lower or equal to the priority.
> 
> Spurious interrupt can happen while releasing interrupt assigned to
> guest (happen during domain destruction). The interaction is roughly
> 
> CPU0                                CPU1
> release_guest_irq(A)
> spin_lock(&desc->lock)
> gic_remove_irq_from_guest
>                                     receive IRQ A
>                                     spin_lock(&desc->lock)
>     desc->handler->shutdown()
>       set_bit(IRQ_DISABLED)
>     desc->handler = &no_irq_type
> spin_unlock(&desc->lock)
>                                     desc->handler->end();
>                                     spin_unlock(&desc->lock)
> 
> Because the no_irq_type.end callback is implemented as a NOP, CPU1 will
> not drop the priority of the interrupt. So the CPU will not be able to
> receive any interrupt route to any guest afterwards.
> 
> The problem can be prevented by dropping the priority and deactivating
> the interrupt via gic_hw_ops->gic_host_irq->end().
> 
> Note that, for now, interrupt used by Xen are safe because it is not
> using no_irq_type on release.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

Hi Juergen,

Can I have your relese ack on this fix?

Cheers,

Stefano


> ---
>  xen/arch/arm/irq.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/irq.c b/xen/arch/arm/irq.c
> index 4a02cc1eba..c51cf333ce 100644
> --- a/xen/arch/arm/irq.c
> +++ b/xen/arch/arm/irq.c
> @@ -44,7 +44,14 @@ static void ack_none(struct irq_desc *irq)
>      printk("unexpected IRQ trap at irq %02x\n", irq->irq);
>  }
>  
> -static void end_none(struct irq_desc *irq) { }
> +static void end_none(struct irq_desc *irq)
> +{
> +    /*
> +     * Still allow a CPU to end an interrupt if we receive a spurious
> +     * interrupt. This will prevent the CPU to lose interrupt forever.
> +     */
> +    gic_hw_ops->gic_host_irq_type->end(irq);
> +}
>  
>  hw_irq_controller no_irq_type = {
>      .typename = "none",
> -- 
> 2.11.0
> 

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