Re: [RFC 09/17] bypass: IRQ bypass manager proto by Alex

Eric Auger
2015-07-03T05:32:28Z

Hi Feng,
On 07/03/2015 04:16 AM, Wu, Feng wrote:
>
>
>> -----Original Message-----
>> From: Eric Auger [mailto:eric.auger@linaro.org]
>> Sent: Thursday, July 02, 2015 9:17 PM
>> To: eric.auger@st.com; eric.auger@linaro.org;
>> linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
>> kvm@vger.kernel.org; christoffer.dall@linaro.org; marc.zyngier@arm.com;
>> alex.williamson@redhat.com; pbonzini@redhat.com; avi.kivity@gmail.com;
>> mtosatti@redhat.com; Wu, Feng; joro@8bytes.org;
>> b.reynal@virtualopensystems.com
>> Cc: linux-kernel@vger.kernel.org; patches@linaro.org
>> Subject: [RFC 09/17] bypass: IRQ bypass manager proto by Alex
>>
>> From: Alex Williamson <alex.williamson@redhat.com>
>>
>> There are plenty of details to be filled in, but I think the basics
>> looks something like the code below. The IRQ bypass manager just
>> defines a pair of structures, one for interrupt producers and one for
>> interrupt consumers. I'm certain that we'll need more callbacks than
>> I've defined below, but figuring out what those should be for the best
>> abstraction is the hardest part of this idea. The manager provides both
>> registration and de-registration interfaces for both types of objects
>> and keeps lists for each, protected by a lock. The manager doesn't even
>> really need to know what the match token is, but I assume for our
>> purposes it will be an eventfd_ctx.
>>
>> On the vfio side, the producer struct would be embedded in the
>> vfio_pci_irq_ctx struct. KVM would probably embed the consumer struct
>> in _irqfd. As I've coded below, the IRQ bypass manager calls the
>> consumer callbacks, so the producer struct would need fields or
>> callbacks to provide the consumer the info it needs. AIUI the Posted
>> Interrupt model, VFIO only needs to provide data to the consumer. For
>> IRQ Forwarding, I think the producer needs to be informed when bypass is
>> active to model the incoming interrupt as edge vs level.
>>
>> I've prototyped the base IRQ bypass manager here as static, but I don't
>> see any reason it couldn't be a module that's loaded by dependency when
>> either vfio-pci or kvm-intel is loaded (or other producer/consumer
>> objects).
>>
>> Is this a reasonable starting point to craft the additional fields and
>> callbacks and interaction of who calls who that we need to support
>> Posted Interrupts and IRQ Forwarding? Is the AMD version of this still
>> alive? Thanks,
>>
>> Alex
>
> In fact, I also implement a RFC patch for this new framework. I am
> thinking, can we discuss all the requirements for irq forwarding and
> posted interrupts, and make it a separate patchset as a general
> layer? Then we can continue to push arch specific stuff, it is more
> clear and easy.

Sure. I intend to respin today according to Paolo's directives and I
will put common patches in a separate series. Let's see next week with
Alex how he prefers things to be handled.

Best Regards

Eric

>
> Thanks,
> Feng
>
>> ---
>> arch/x86/kvm/Kconfig | 1 +
>> drivers/vfio/pci/Kconfig | 1 +
>> drivers/vfio/pci/vfio_pci_intrs.c | 6 ++
>> include/linux/irqbypass.h | 23 ++++++++
>> kernel/irq/Kconfig | 3 +
>> kernel/irq/Makefile | 1 +
>> kernel/irq/bypass.c | 116
>> ++++++++++++++++++++++++++++++++++++++
>> virt/kvm/eventfd.c | 4 ++
>> 8 files changed, 155 insertions(+)
>> create mode 100644 include/linux/irqbypass.h
>> create mode 100644 kernel/irq/bypass.c
>>
>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>> index d8a1d56..86d0d77 100644
>> --- a/arch/x86/kvm/Kconfig
>> +++ b/arch/x86/kvm/Kconfig
>> @@ -61,6 +61,7 @@ config KVM_INTEL
>> depends on KVM
>> # for perf_guest_get_msrs():
>> depends on CPU_SUP_INTEL
>> + select IRQ_BYPASS_MANAGER
>> ---help---
>> Provides support for KVM on Intel processors equipped with the VT
>> extensions.
>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
>> index 579d83b..02912f1 100644
>> --- a/drivers/vfio/pci/Kconfig
>> +++ b/drivers/vfio/pci/Kconfig
>> @@ -2,6 +2,7 @@ config VFIO_PCI
>> tristate "VFIO support for PCI devices"
>> depends on VFIO && PCI && EVENTFD
>> select VFIO_VIRQFD
>> + select IRQ_BYPASS_MANAGER
>> help
>> Support for the PCI VFIO bus driver. This is required to make
>> use of PCI drivers using the VFIO framework.
>> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
>> index 1f577b4..4e053be 100644
>> --- a/drivers/vfio/pci/vfio_pci_intrs.c
>> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
>> @@ -181,6 +181,7 @@ static int vfio_intx_set_signal(struct vfio_pci_device
>> *vdev, int fd)
>>
>> if (vdev->ctx[0].trigger) {
>> free_irq(pdev->irq, vdev);
>> + /* irq_bypass_unregister_producer(); */
>> kfree(vdev->ctx[0].name);
>> eventfd_ctx_put(vdev->ctx[0].trigger);
>> vdev->ctx[0].trigger = NULL;
>> @@ -214,6 +215,8 @@ static int vfio_intx_set_signal(struct vfio_pci_device
>> *vdev, int fd)
>> return ret;
>> }
>>
>> + /* irq_bypass_register_producer(); */
>> +
>> /*
>> * INTx disable will stick across the new irq setup,
>> * disable_irq won't.
>> @@ -319,6 +322,7 @@ static int vfio_msi_set_vector_signal(struct
>> vfio_pci_device *vdev,
>>
>> if (vdev->ctx[vector].trigger) {
>> free_irq(irq, vdev->ctx[vector].trigger);
>> + /* irq_bypass_unregister_producer(); */
>> kfree(vdev->ctx[vector].name);
>> eventfd_ctx_put(vdev->ctx[vector].trigger);
>> vdev->ctx[vector].trigger = NULL;
>> @@ -360,6 +364,8 @@ static int vfio_msi_set_vector_signal(struct
>> vfio_pci_device *vdev,
>> return ret;
>> }
>>
>> + /* irq_bypass_register_producer(); */
>> +
>> vdev->ctx[vector].trigger = trigger;
>>
>> return 0;
>> diff --git a/include/linux/irqbypass.h b/include/linux/irqbypass.h
>> new file mode 100644
>> index 0000000..718508e
>> --- /dev/null
>> +++ b/include/linux/irqbypass.h
>> @@ -0,0 +1,23 @@
>> +#ifndef IRQBYPASS_H
>> +#define IRQBYPASS_H
>> +
>> +#include <linux/list.h>
>> +
>> +struct irq_bypass_producer {
>> + struct list_head node;
>> + void *token;
>> + /* TBD */
>> +};
>> +
>> +struct irq_bypass_consumer {
>> + struct list_head node;
>> + void *token;
>> + void (*add_producer)(struct irq_bypass_producer *);
>> + void (*del_producer)(struct irq_bypass_producer *);
>> +};
>> +
>> +int irq_bypass_register_producer(struct irq_bypass_producer *);
>> +void irq_bypass_unregister_producer(struct irq_bypass_producer *);
>> +int irq_bypass_register_consumer(struct irq_bypass_consumer *);
>> +void irq_bypass_unregister_consumer(struct irq_bypass_consumer *);
>> +#endif /* IRQBYPASS_H */
>> diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
>> index 9a76e3b..4502cdc 100644
>> --- a/kernel/irq/Kconfig
>> +++ b/kernel/irq/Kconfig
>> @@ -100,4 +100,7 @@ config SPARSE_IRQ
>>
>> If you don't know what to do here, say N.
>>
>> +config IRQ_BYPASS_MANAGER
>> + bool
>> +
>> endmenu
>> diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
>> index d121235..a30ed77 100644
>> --- a/kernel/irq/Makefile
>> +++ b/kernel/irq/Makefile
>> @@ -7,3 +7,4 @@ obj-$(CONFIG_PROC_FS) += proc.o
>> obj-$(CONFIG_GENERIC_PENDING_IRQ) += migration.o
>> obj-$(CONFIG_PM_SLEEP) += pm.o
>> obj-$(CONFIG_GENERIC_MSI_IRQ) += msi.o
>> +obj-$(CONFIG_IRQ_BYPASS_MANAGER) += bypass.o
>> diff --git a/kernel/irq/bypass.c b/kernel/irq/bypass.c
>> new file mode 100644
>> index 0000000..5d0f92b
>> --- /dev/null
>> +++ b/kernel/irq/bypass.c
>> @@ -0,0 +1,116 @@
>> +/*
>> + * IRQ offload/bypass manager
>> + *
>> + * Various virtualization hardware acceleration techniques allow bypassing
>> + * or offloading interrupts receieved from devices around the host kernel.
>> + * Posted Interrupts on Intel VT-d systems can allow interrupts to be
>> + * recieved directly by a virtual machine. ARM IRQ Forwarding can allow
>> + * level triggered device interrupts to be de-asserted directly by the VM.
>> + * This manager allows interrupt producers and consumers to find each other
>> + * to enable this sort of bypass.
>> + */
>> +
>> +#include <linux/irqbypass.h>
>> +#include <linux/list.h>
>> +#include <linux/module.h>
>> +#include <linux/mutex.h>
>> +
>> +static LIST_HEAD(producers);
>> +static LIST_HEAD(consumers);
>> +static DEFINE_MUTEX(lock);
>> +
>> +int irq_bypass_register_producer(struct irq_bypass_producer *producer)
>> +{
>> + struct irq_bypass_producer *tmp;
>> + struct irq_bypass_consumer *consumer;
>> + int ret = 0;
>> +
>> + mutex_lock(&lock);
>> +
>> + list_for_each_entry(tmp, &producers, node) {
>> + if (tmp->token == producer->token) {
>> + ret = -EINVAL;
>> + goto unlock;
>> + }
>> + }
>> +
>> + list_add(&producer->node, &producers);
>> +
>> + list_for_each_entry(consumer, &consumers, node) {
>> + if (consumer->token == producer->token) {
>> + consumer->add_producer(producer);
>> + break;
>> + }
>> + }
>> +unlock:
>> + mutex_unlock(&lock);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(irq_bypass_register_producer);
>> +
>> +void irq_bypass_unregister_producer(struct irq_bypass_producer *producer)
>> +{
>> + struct irq_bypass_consumer *consumer;
>> +
>> + mutex_lock(&lock);
>> +
>> + list_for_each_entry(consumer, &consumers, node) {
>> + if (consumer->token == producer->token) {
>> + consumer->del_producer(producer);
>> + break;
>> + }
>> + }
>> +
>> + list_del(&producer->node);
>> +
>> + mutex_unlock(&lock);
>> +}
>> +EXPORT_SYMBOL_GPL(irq_bypass_unregister_producer);
>> +
>> +int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer)
>> +{
>> + struct irq_bypass_consumer *tmp;
>> + struct irq_bypass_producer *producer;
>> + int ret = 0;
>> +
>> + mutex_lock(&lock);
>> +
>> + list_for_each_entry(tmp, &consumers, node) {
>> + if (tmp->token == consumer->token) {
>> + ret = -EINVAL;
>> + goto unlock;
>> + }
>> + }
>> +
>> + list_add(&consumer->node, &consumers);
>> +
>> + list_for_each_entry(producer, &producers, node) {
>> + if (producer->token == consumer->token) {
>> + consumer->add_producer(producer);
>> + break;
>> + }
>> + }
>> +unlock:
>> + mutex_unlock(&lock);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(irq_bypass_register_consumer);
>> +
>> +void irq_bypass_unregister_consumer(struct irq_bypass_consumer
>> *consumer)
>> +{
>> + struct irq_bypass_producer *producer;
>> +
>> + mutex_lock(&lock);
>> +
>> + list_for_each_entry(producer, &producers, node) {
>> + if (producer->token == consumer->token) {
>> + consumer->del_producer(producer);
>> + break;
>> + }
>> + }
>> +
>> + list_del(&consumer->node);
>> +
>> + mutex_unlock(&lock);
>> +}
>> +EXPORT_SYMBOL_GPL(irq_bypass_unregister_consumer);
>> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
>> index 9ff4193..f3da161 100644
>> --- a/virt/kvm/eventfd.c
>> +++ b/virt/kvm/eventfd.c
>> @@ -429,6 +429,8 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd
>> *args)
>> */
>> fdput(f);
>>
>> + /* irq_bypass_register_consumer(); */
>> +
>> return 0;
>>
>> fail:
>> @@ -528,6 +530,8 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd
>> *args)
>> struct _irqfd *irqfd, *tmp;
>> struct eventfd_ctx *eventfd;
>>
>> + /* irq_bypass_unregister_consumer() */
>> +
>> eventfd = eventfd_ctx_fdget(args->fd);
>> if (IS_ERR(eventfd))
>> return PTR_ERR(eventfd);
>> --
>> 1.9.1
>