linux-kernel - Re: [PATCH v5 13/17] irqdomain: irq_domain_check_msi

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Date:   Wed, 4 Jan 2017 15:11:56 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>, eric.auger.pro@...il.com,
        christoffer.dall@...aro.org, robin.murphy@....com,
        alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org,
        tglx@...utronix.de, jason@...edaemon.net,
        linux-arm-kernel@...ts.infradead.org
Cc:     kvm@...r.kernel.org, drjones@...hat.com,
        linux-kernel@...r.kernel.org, pranav.sawargaonkar@...il.com,
        iommu@...ts.linux-foundation.org, punit.agrawal@....com,
        diana.craciun@....com, gpkulkarni@...il.com,
        shankerd@...eaurora.org, bharat.bhushan@....com,
        geethasowjanya.akula@...il.com
Subject: Re: [PATCH v5 13/17] irqdomain: irq_domain_check_msi_remap

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@...hat.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?

Thanks

Eric
> 
> Thanks,
> 
> 	M.
>