Date:   Fri, 6 Jan 2017 04:27:03 +0000
From:   Bharat Bhushan <bharat.bhushan@....com>
To:     Auger Eric <eric.auger@...hat.com>,
        Marc Zyngier <marc.zyngier@....com>,
        "eric.auger.pro@...il.com" <eric.auger.pro@...il.com>,
        "christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     "drjones@...hat.com" <drjones@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "punit.agrawal@....com" <punit.agrawal@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "geethasowjanya.akula@...il.com" <geethasowjanya.akula@...il.com>,
        "Diana Madalina Craciun" <diana.craciun@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "pranav.sawargaonkar@...il.com" <pranav.sawargaonkar@...il.com>,
        "shankerd@...eaurora.org" <shankerd@...eaurora.org>,
        "gpkulkarni@...il.com" <gpkulkarni@...il.com>
Subject: RE: [PATCH v5 13/17] irqdomain: irq_domain_check_msi_remap

Hi Mark,

> -----Original Message-----
> From: Auger Eric [mailto:eric.auger@...hat.com]
> Sent: Thursday, January 05, 2017 5:39 PM
> 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: drjones@...hat.com; kvm@...r.kernel.org; punit.agrawal@....com;
> linux-kernel@...r.kernel.org; geethasowjanya.akula@...il.com; Diana
> Madalina Craciun <diana.craciun@....com>; iommu@...ts.linux-
> foundation.org; pranav.sawargaonkar@...il.com; Bharat Bhushan
> <bharat.bhushan@....com>; shankerd@...eaurora.org;
> gpkulkarni@...il.com
> Subject: Re: [PATCH v5 13/17] irqdomain: irq_domain_check_msi_remap
> 
> Hi Marc,
> 
> On 05/01/2017 12:57, Marc Zyngier wrote:
> > On 05/01/17 11:29, Auger Eric wrote:
> >> Hi Marc,
> >>
> >> On 05/01/2017 12:25, Marc Zyngier wrote:
> >>> On 05/01/17 10:45, Auger Eric wrote:
> >>>> 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@...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?
> >>>>>
> >>>>> 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)?
> >> was mentioning platform_msi_create_*device*_domain.
> >> it calls irq_domain_create_hierarchy and looks to be MSI irq domain
> >> related. But I don't have a full understanding of the whole irq
> >> domain hierarchy.
> >
> > Ah, sorry - I blame the ARM coffee.
> >
> > This function builds a domain for a single device on top of the MSI
> > domain that has been already created (see the dev->msi_domain passed
> > to irq_domain_create_hierarchy). The structure looks like this:
> >
> > device-domain -> platform MSI domain -> HW MSI domain -> whatever
> >
> > So what we're *really* interested in is the platform MSI domain, which
> > is going to carry the IRQ_DOMAIN_FLAG_MSI flag. The device-domain only
> > describes a portion of it, and can safely be ignored.
> >
> > In the end, what matters for this patch is that we can prove that from
> > any domain carrying the IRQ_DOMAIN_FLAG_MSI flag, we can find a
> domain
> > carrying the IRQ_DOMAIN_FLAG_MSI_REMAP flag. If that property holds,
> > we're safe. Otherwise, we disable the Guest MSI feature.
> >
> > Does it make sense?
> Yes it makes sense. Thank you for the explanation!

If I understood correctly then the domain hierarchy is 

 -> "gic-irq-domain"
	 -> "gic-its-irq-domain"
		-> "platform-msi-domain"
		-> "pci-msi-domain"
		->  "fsl-mc-msi-domain"

"gic-its-irq-domain" carries IRQ_DOMAIN_FLAG_MSI_REMAP

So we need to look for the IRQ_DOMAIN_FLAG_MSI_REMAP flag in "gic-its-irq-domain" when doing safety check for "platform/pci/fsl-mc"-msi-irqdomain,  is this what you mentioned?

Can we can pass this flags from "gic-its-irq-domain" to "platform/pci/fsl-mc"-msi-irqdomain during domain creation?

Thanks
-Bharat

> 
> Eric
> >
> > Thanks,
> >
> > 	M.
> >

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