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Message-ID: <a574e969-b46d-94fb-e4c2-646a37b17122@redhat.com>
Date: Thu, 5 Jan 2017 13:08:40 +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: drjones@...hat.com, kvm@...r.kernel.org, punit.agrawal@....com,
linux-kernel@...r.kernel.org, geethasowjanya.akula@...il.com,
diana.craciun@....com, iommu@...ts.linux-foundation.org,
pranav.sawargaonkar@...il.com, 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!
Eric
>
> Thanks,
>
> M.
>
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