Re: [RFC PATCH] irq: IRQ bypass manager

From: Alex Williamson
Date: Wed Jul 08 2015 - 08:54:18 EST

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On Wed, 2015-07-08 at 12:22 +0000, Wu, Feng wrote:
>
>
> > -----Original Message-----
> > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> > Sent: Wednesday, July 08, 2015 5:40 AM
> > To: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
> > Cc: eric.auger@xxxxxx; eric.auger@xxxxxxxxxx; joro@xxxxxxxxxx;
> > avi.kivity@xxxxxxxxx; pbonzini@xxxxxxxxxx; Wu, Feng
> > Subject: [RFC PATCH] irq: IRQ bypass manager
> >
> > When a physical I/O device is assigned to a virtual machine through
> > facilities like VFIO and KVM, the interrupt for the device generally
> > bounces through the host system before being injected into the VM.
> > However, hardware technologies exist that often allow the host to be
> > bypassed for some of these scenarios. Intel Posted Interrupts allow
> > the specified physical edge interrupts to be directly injected into a
> > guest when delivered to a physical processor while the vCPU is
> > running. ARM IRQ Forwarding allows the hypervisor to handle level
> > triggered device interrupts as edge interrupts, by giving the guest
> > control of de-asserting and unmasking the interrupt line.
> >
> > The IRQ bypass manager here is meant to provide the shim to connect
> > interrupt producers, generally the host physical device driver, with
> > interrupt consumers, generally the hypervisor, in order to configure
> > these bypass mechanism. To do this, we base the connection on a
> > shared, opaque token. For KVM-VFIO this is expected to be an
> > eventfd_ctx since this is the connection we already use to connect an
> > eventfd to an irqfd on the in-kernel path. When a producer and
> > consumer with matching tokens is found, callbacks via both registered
> > participants allow the bypass facilities to be automatically enabled.
>
> My Pi patches can work well based on this one and the one Eric sent
> out earlier. Alex, what should we do in the next step to speed up the
> upstreaming process?

Hi Feng,

Post the patches. Define how the update() callback is used. Help to
address the issues I've outlined below. Thanks,

Alex

> >
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> > ---
> >
> > This is the current draft of the IRQ bypass manager, I've made the
> > following changes:
> >
> > - Incorporated Eric's extensions (I would welcome Sign-offs from all
> > involved in the development, especially Eric - I've gone ahead and
> > added Linaro copyright for the contributions so far)
> > - Module support with module reference tracking
> > - might_sleep() as suggested by Paolo
> > - kerneldoc as suggested by Paolo
> > - Renamed file s/bypass/irqbypass/ because a module named "bypass"
> > is strange
> >
> > Issues:
> > - The update() callback is defined but not used
> > - We can't have *all* the callbacks be optional. I assume add/del
> > are required
> > - Naming consistency, stop is to start as suspend is to resume, not
> > stop/resume
> > - Callback descriptions including why we need separate stop/start
> > hooks when it seems like the callee could reasonably assume such
> > around the add/del callbacks
> > - Need functional prototypes for both PI and forwarding
> >
> > include/linux/irqbypass.h | 75 ++++++++++++++++
> > kernel/irq/Kconfig | 3 +
> > kernel/irq/Makefile | 1
> > kernel/irq/irqbypass.c | 206
> > +++++++++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 285 insertions(+)
> > create mode 100644 include/linux/irqbypass.h
> > create mode 100644 kernel/irq/irqbypass.c
> >
> > diff --git a/include/linux/irqbypass.h b/include/linux/irqbypass.h
> > new file mode 100644
> > index 0000000..cc7ce45
> > --- /dev/null
> > +++ b/include/linux/irqbypass.h
> > @@ -0,0 +1,75 @@
> > +/*
> > + * IRQ offload/bypass manager
> > + *
> > + * Copyright (C) 2015 Red Hat, Inc.
> > + * Copyright (c) 2015 Linaro Ltd.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +#ifndef IRQBYPASS_H
> > +#define IRQBYPASS_H
> > +
> > +#include <linux/list.h>
> > +
> > +struct irq_bypass_consumer;
> > +
> > +/**
> > + * struct irq_bypass_producer - IRQ bypass producer definition
> > + * @node: IRQ bypass manager private list management
> > + * @token: opaque token to match between producer and consumer
> > + * @irq: Linux IRQ number for the producer device
> > + * @stop:
> > + * @resume:
> > + * @add_consumer:
> > + * @del_consumer:
> > + *
> > + * The IRQ bypass producer structure represents an interrupt source for
> > + * participation in possible host bypass, for instance an interrupt vector
> > + * for a physical device assigned to a VM.
> > + */
> > +struct irq_bypass_producer {
> > + struct list_head node;
> > + void *token;
> > + int irq; /* linux irq */
> > + void (*stop)(struct irq_bypass_producer *);
> > + void (*resume)(struct irq_bypass_producer *);
> > + void (*add_consumer)(struct irq_bypass_producer *,
> > + struct irq_bypass_consumer *);
> > + void (*del_consumer)(struct irq_bypass_producer *,
> > + struct irq_bypass_consumer *);
> > +};
> > +
> > +/**
> > + * struct irq_bypass_consumer - IRQ bypass consumer definition
> > + * @node: IRQ bypass manager private list management
> > + * @token: opaque token to match between producer and consumer
> > + * @stop:
> > + * @resume:
> > + * @add_consumer:
> > + * @del_consumer:
> > + * @update:
> > + *
> > + * The IRQ bypass consumer structure represents an interrupt sink for
> > + * participation in possible host bypass, for instance a hypervisor may
> > + * support offloads to allow bypassing the host entirely or offload
> > + * portions of the interrupt handling to the VM.
> > + */
> > +struct irq_bypass_consumer {
> > + struct list_head node;
> > + void *token;
> > + void (*stop)(struct irq_bypass_consumer *);
> > + void (*resume)(struct irq_bypass_consumer *);
> > + void (*add_producer)(struct irq_bypass_consumer *,
> > + struct irq_bypass_producer *);
> > + void (*del_producer)(struct irq_bypass_consumer *,
> > + struct irq_bypass_producer *);
> > + void (*update)(struct irq_bypass_consumer *);
> > +};
> > +
> > +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..de5afe3 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
> > + tristate
> > +
> > endmenu
> > diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
> > index d121235..a6cfec7 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) += irqbypass.o
> > diff --git a/kernel/irq/irqbypass.c b/kernel/irq/irqbypass.c
> > new file mode 100644
> > index 0000000..3fd828d
> > --- /dev/null
> > +++ b/kernel/irq/irqbypass.c
> > @@ -0,0 +1,206 @@
> > +/*
> > + * IRQ offload/bypass manager
> > + *
> > + * Copyright (C) 2015 Red Hat, Inc.
> > + * Copyright (c) 2015 Linaro Ltd.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * Various virtualization hardware acceleration techniques allow bypassing
> > + * or offloading interrupts received from devices around the host kernel.
> > + * Posted Interrupts on Intel VT-d systems can allow interrupts to be
> > + * received 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>
> > +
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_DESCRIPTION("IRQ bypass manager utility module");
> > +
> > +static LIST_HEAD(producers);
> > +static LIST_HEAD(consumers);
> > +static DEFINE_MUTEX(lock);
> > +
> > +/* @lock must be held when calling connect */
> > +static void __connect(struct irq_bypass_producer *prod,
> > + struct irq_bypass_consumer *cons)
> > +{
> > + if (prod->stop)
> > + prod->stop(prod);
> > + if (cons->stop)
> > + cons->stop(cons);
> > + if (prod->add_consumer)
> > + prod->add_consumer(prod, cons);
> > + if (cons->add_producer)
> > + cons->add_producer(cons, prod);
> > + if (cons->resume)
> > + cons->resume(cons);
> > + if (prod->resume)
> > + prod->resume(prod);
> > +}
> > +
> > +/* @lock must be held when calling disconnect */
> > +static void __disconnect(struct irq_bypass_producer *prod,
> > + struct irq_bypass_consumer *cons)
> > +{
> > + if (prod->stop)
> > + prod->stop(prod);
> > + if (cons->stop)
> > + cons->stop(cons);
> > + if (cons->del_producer)
> > + cons->del_producer(cons, prod);
> > + if (prod->del_consumer)
> > + prod->del_consumer(prod, cons);
> > + if (cons->resume)
> > + cons->resume(cons);
> > + if (prod->resume)
> > + prod->resume(prod);
> > +}
> > +
> > +/**
> > + * irq_bypass_register_producer - register IRQ bypass producer
> > + * @producer: pointer to producer structure
> > + *
> > + * Add the provided IRQ producer to the list of producers and connect
> > + * with any matching tokens found on the IRQ consumers list.
> > + */
> > +int irq_bypass_register_producer(struct irq_bypass_producer *producer)
> > +{
> > + struct irq_bypass_producer *tmp;
> > + struct irq_bypass_consumer *consumer;
> > +
> > + might_sleep();
> > +
> > + if (!try_module_get(THIS_MODULE))
> > + return -ENODEV;
> > +
> > + mutex_lock(&lock);
> > +
> > + list_for_each_entry(tmp, &producers, node) {
> > + if (tmp->token == producer->token) {
> > + mutex_unlock(&lock);
> > + module_put(THIS_MODULE);
> > + return -EINVAL;
> > + }
> > + }
> > +
> > + list_add(&producer->node, &producers);
> > +
> > + list_for_each_entry(consumer, &consumers, node) {
> > + if (consumer->token == producer->token) {
> > + __connect(producer, consumer);
> > + break;
> > + }
> > + }
> > +
> > + mutex_unlock(&lock);
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(irq_bypass_register_producer);
> > +
> > +/**
> > + * irq_bypass_unregister_producer - unregister IRQ bypass producer
> > + * @producer: pointer to producer structure
> > + *
> > + * Remove a previously registered IRQ producer from the list of producers
> > + * and disconnected from any connected IRQ consumers.
> > + */
> > +void irq_bypass_unregister_producer(struct irq_bypass_producer *producer)
> > +{
> > + struct irq_bypass_consumer *consumer;
> > +
> > + might_sleep();
> > +
> > + mutex_lock(&lock);
> > +
> > + list_for_each_entry(consumer, &consumers, node) {
> > + if (consumer->token == producer->token) {
> > + __disconnect(producer, consumer);
> > + break;
> > + }
> > + }
> > +
> > + list_del(&producer->node);
> > +
> > + mutex_unlock(&lock);
> > + module_put(THIS_MODULE);
> > +}
> > +EXPORT_SYMBOL_GPL(irq_bypass_unregister_producer);
> > +
> > +/**
> > + * irq_bypass_register_consumer - register IRQ bypass consumer
> > + * @consumer: pointer to consumer structure
> > + *
> > + * Add the provided IRQ consumer to the list of consumers and connect
> > + * with any matching tokens found on the IRQ producer list.
> > + */
> > +int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer)
> > +{
> > + struct irq_bypass_consumer *tmp;
> > + struct irq_bypass_producer *producer;
> > +
> > + might_sleep();
> > +
> > + if (!try_module_get(THIS_MODULE))
> > + return -ENODEV;
> > +
> > + mutex_lock(&lock);
> > +
> > + list_for_each_entry(tmp, &consumers, node) {
> > + if (tmp->token == consumer->token) {
> > + mutex_unlock(&lock);
> > + module_put(THIS_MODULE);
> > + return -EINVAL;
> > + }
> > + }
> > +
> > + list_add(&consumer->node, &consumers);
> > +
> > + list_for_each_entry(producer, &producers, node) {
> > + if (producer->token == consumer->token) {
> > + __connect(producer, consumer);
> > + break;
> > + }
> > + }
> > +
> > + mutex_unlock(&lock);
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(irq_bypass_register_consumer);
> > +
> > +/**
> > + * irq_bypass_unregister_consumer - unregister IRQ bypass consumer
> > + * @consumer: pointer to consumer structure
> > + *
> > + * Remove a previously registered IRQ consumer from the list of consumers
> > + * and disconnected from any connected IRQ producers.
> > + */
> > +void irq_bypass_unregister_consumer(struct irq_bypass_consumer
> > *consumer)
> > +{
> > + struct irq_bypass_producer *producer;
> > +
> > + might_sleep();
> > +
> > + mutex_lock(&lock);
> > +
> > + list_for_each_entry(producer, &producers, node) {
> > + if (producer->token == consumer->token) {
> > + __disconnect(producer, consumer);
> > + break;
> > + }
> > + }
> > +
> > + list_del(&consumer->node);
> > +
> > + mutex_unlock(&lock);
> > + module_put(THIS_MODULE);
> > +}
> > +EXPORT_SYMBOL_GPL(irq_bypass_unregister_consumer);
>

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Next message: Frederic Weisbecker: "Re: [PATCH 2/3] kmod: Add up-to-date explanations on the purpose of each asynchronous levels"
Previous message: Prarit Bhargava: "Re: [PATCH 2/2] serial: 8250: Allow to skip autoconfig_irq() for a console"
In reply to: Wu, Feng: "RE: [RFC PATCH] irq: IRQ bypass manager"
Next in thread: Eric Auger: "Re: [RFC PATCH] irq: IRQ bypass manager"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]