Re: [PATCH v5 13/17] irqdomain: irq_domain_check_msi_remap

[Auger Eric <eric.auger@redhat.com>]

Hi Marc,

On 04/01/2017 16:27, Marc Zyngier wrote:
> On 04/01/17 14:11, Auger Eric wrote:
>> Hi Marc,
>>
>> On 04/01/2017 14:46, Marc Zyngier wrote:
>>> Hi Eric,
>>>
>>> On 04/01/17 13:32, Eric Auger wrote:
>>>> This new function checks whether all platform and PCI
>>>> MSI 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@redhat.com>
>>>>
>>>> ---
>>>>
>>>> v4 -> v5:
>>>> - Handle DOMAIN_BUS_FSL_MC_MSI domains
>>>> - Check parents
>>>> ---
>>>>  include/linux/irqdomain.h |  1 +
>>>>  kernel/irq/irqdomain.c    | 41 +++++++++++++++++++++++++++++++++++++++++
>>>>  2 files changed, 42 insertions(+)
>>>>
>>>> diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
>>>> index ab017b2..281a40f 100644
>>>> --- a/include/linux/irqdomain.h
>>>> +++ b/include/linux/irqdomain.h
>>>> @@ -219,6 +219,7 @@ 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 8c0a0ae..700caea 100644
>>>> --- a/kernel/irq/irqdomain.c
>>>> +++ b/kernel/irq/irqdomain.c
>>>> @@ -278,6 +278,47 @@ struct irq_domain *irq_find_matching_fwspec(struct irq_fwspec *fwspec,
>>>>  EXPORT_SYMBOL_GPL(irq_find_matching_fwspec);
>>>>  
>>>>  /**
>>>> + * irq_domain_is_msi_remap - Check if @domain or any parent
>>>> + * has MSI remapping support
>>>> + * @domain: domain pointer
>>>> + */
>>>> +static bool irq_domain_is_msi_remap(struct irq_domain *domain)
>>>> +{
>>>> +	struct irq_domain *h = domain;
>>>> +
>>>> +	for (; h; h = h->parent) {
>>>> +		if (h->flags & IRQ_DOMAIN_FLAG_MSI_REMAP)
>>>> +			return true;
>>>> +	}
>>>> +	return false;
>>>> +}
>>>> +
>>>> +/**
>>>> + * irq_domain_check_msi_remap() - Checks 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 (((h->bus_token & DOMAIN_BUS_PCI_MSI) ||
>>>> +		     (h->bus_token & DOMAIN_BUS_PLATFORM_MSI) ||
>>>> +		     (h->bus_token & DOMAIN_BUS_FSL_MC_MSI)) &&
>>>> +		     !irq_domain_is_msi_remap(h)) {
>>>
>>> (h->bus_token & DOMAIN_BUS_PCI_MSI) and co looks quite wrong. bus_token
>>> is not a bitmap, and DOMAIN_BUS_* not a single bit value (see enum
>>> irq_domain_bus_token). Surely this should read
>>> (h->bus_token == DOMAIN_BUS_PCI_MSI).
>> Oh I did not notice that. Thanks.
>>
>> Any other comments on the irqdomain side? Do you think the current
>> approach consisting in looking at those bus tokens and their parents
>> looks good?
> 
> To be completely honest, I don't like it much, as having to enumerate
> all the bus types can come up with could become quite a burden in the
> long run. I'd rather be able to identify MSI capable domains by
> construction. I came up with the following approach (fully untested):
> 
> diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
> index 281a40f..7779796 100644
> --- a/include/linux/irqdomain.h
> +++ b/include/linux/irqdomain.h
> @@ -183,8 +183,11 @@ enum {
>  	/* Irq domain is an IPI domain with single virq */
>  	IRQ_DOMAIN_FLAG_IPI_SINGLE	= (1 << 3),
>  
> +	/* Irq domain implements MSIs */
> +	IRQ_DOMAIN_FLAG_MSI		= (1 << 4),
> +
>  	/* Irq domain is MSI remapping capable */
> -	IRQ_DOMAIN_FLAG_MSI_REMAP	= (1 << 4),
> +	IRQ_DOMAIN_FLAG_MSI_REMAP	= (1 << 5),
>  
>  	/*
>  	 * Flags starting from IRQ_DOMAIN_FLAG_NONCORE are reserved
> @@ -450,6 +453,11 @@ static inline bool irq_domain_is_ipi_single(struct irq_domain *domain)
>  {
>  	return domain->flags & IRQ_DOMAIN_FLAG_IPI_SINGLE;
>  }
> +
> +static inline bool irq_domain_is_msi(struct irq_domain *domain)
> +{
> +	return domain->flags & IRQ_DOMAIN_FLAG_MSI;
> +}
>  #else	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
>  static inline void irq_domain_activate_irq(struct irq_data *data) { }
>  static inline void irq_domain_deactivate_irq(struct irq_data *data) { }
> @@ -481,6 +489,11 @@ static inline bool irq_domain_is_ipi_single(struct irq_domain *domain)
>  {
>  	return false;
>  }
> +
> +static inline bool irq_domain_is_msi(struct irq_domain *domain)
> +{
> +	return false;
> +}
>  #endif	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
>  
>  #else /* CONFIG_IRQ_DOMAIN */
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index 700caea..33b6921 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -304,10 +304,7 @@ bool irq_domain_check_msi_remap(void)
>  
>  	mutex_lock(&irq_domain_mutex);
>  	list_for_each_entry(h, &irq_domain_list, link) {
> -		if (((h->bus_token & DOMAIN_BUS_PCI_MSI) ||
> -		     (h->bus_token & DOMAIN_BUS_PLATFORM_MSI) ||
> -		     (h->bus_token & DOMAIN_BUS_FSL_MC_MSI)) &&
> -		     !irq_domain_is_msi_remap(h)) {
> +		if (irq_domain_is_msi(h) && !irq_domain_is_msi_remap(h)) {
>  			ret = false;
>  			goto out;
>  		}
> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> index ee23006..b637263 100644
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -270,7 +270,7 @@ struct irq_domain *msi_create_irq_domain(struct fwnode_handle *fwnode,
>  	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
>  		msi_domain_update_chip_ops(info);
>  
> -	return irq_domain_create_hierarchy(parent, 0, 0, fwnode,
> +	return irq_domain_create_hierarchy(parent, IRQ_DOMAIN_FLAG_MSI, 0, fwnode,
>  					   &msi_domain_ops, info);
>  }
>  
> 
> 
> Thoughts?

Don't we need to set the IRQ_DOMAIN_FLAG_MSI flag in
platform_msi_create_device_domain too (drivers/base/platform-msi.c)?

Thanks

Eric
> 
> 	M.
>