Re: [PATCH v8 14/18] irqdomain: irq_domain_check_msi_remap

[Tomasz Nowicki <tn-nYOzD4b6Jr9Wk0Htik3J/w@public.gmane.org>]

On 11.01.2017 10:41, Eric Auger wrote:
> This new function checks whether all MSI irq domains
> implement IRQ remapping. This is useful to understand
> whether VFIO passthrough is safe with respect to interrupts.
>
> On ARM typically an MSI controller can sit downstream
> to the IOMMU without preventing VFIO passthrough.
> As such any assigned device can write into the MSI doorbell.
> In case the MSI controller implements IRQ remapping, assigned
> devices will not be able to trigger interrupts towards the
> host. On the contrary, the assignment must be emphasized as
> unsafe with respect to interrupts.
>
> Signed-off-by: Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: Marc Zyngier <marc.zyngier-5wv7dgnIgG8@public.gmane.org>
>
> ---
> v7 -> v8:
> - remove goto in irq_domain_check_msi_remap
> - Added Marc's R-b
>
> v5 -> v6:
> - use irq_domain_hierarchical_is_msi_remap()
> - comment rewording
>
> v4 -> v5:
> - Handle DOMAIN_BUS_FSL_MC_MSI domains
> - Check parents
> ---
>  include/linux/irqdomain.h |  1 +
>  kernel/irq/irqdomain.c    | 22 ++++++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
> index bc2f571..188eced 100644
> --- a/include/linux/irqdomain.h
> +++ b/include/linux/irqdomain.h
> @@ -222,6 +222,7 @@ struct irq_domain *irq_domain_add_legacy(struct device_node *of_node,
>  					 void *host_data);
>  extern struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
>  						   enum irq_domain_bus_token bus_token);
> +extern bool irq_domain_check_msi_remap(void);
>  extern void irq_set_default_host(struct irq_domain *host);
>  extern int irq_domain_alloc_descs(int virq, unsigned int nr_irqs,
>  				  irq_hw_number_t hwirq, int node,
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index 876e131..d889751 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -278,6 +278,28 @@ struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
>  EXPORT_SYMBOL_GPL(irq_find_matching_fwspec);
>
>  /**
> + * irq_domain_check_msi_remap - Check whether all MSI
> + * irq domains implement IRQ remapping
> + */
> +bool irq_domain_check_msi_remap(void)
> +{
> +	struct irq_domain *h;
> +	bool ret = true;
> +
> +	mutex_lock(&irq_domain_mutex);
> +	list_for_each_entry(h, &irq_domain_list, link) {
> +		if (irq_domain_is_msi(h) &&
> +		    !irq_domain_hierarchical_is_msi_remap(h)) {
> +			ret = false;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&irq_domain_mutex);
> +	return ret;
> +}

Above function returns true, even though there is no MSI irq domains. Is 
it intentional ?

Thanks,
Tomasz