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Message-ID: <20101118111037.GB31261@redhat.com>
Date: Thu, 18 Nov 2010 13:10:37 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Avi Kivity <avi@...hat.com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>,
Gleb Natapov <gleb@...hat.com>,
Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
Gregory Haskins <ghaskins@...ell.com>,
Chris Lalancette <clalance@...hat.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] kvm: fast-path msi injection with irqfd
On Thu, Nov 18, 2010 at 01:03:44PM +0200, Avi Kivity wrote:
> On 11/18/2010 12:57 PM, Michael S. Tsirkin wrote:
> >So the following on top will fix it all.
> >Any more comments befpre I bundle it up,
> >test and report?
> >
>
> Nope (not that I can comment on an incremental).
Here it is rolled up.
> I guess I should create an empty Documentation/kvm/locking.txt and
> force everyone else to update it.
Comments near the relevant fields not better?
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a055742..d13ced3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -16,6 +16,7 @@
#include <linux/mm.h>
#include <linux/preempt.h>
#include <linux/msi.h>
+#include <linux/rcupdate.h>
#include <asm/signal.h>
#include <linux/kvm.h>
@@ -206,6 +207,8 @@ struct kvm {
struct mutex irq_lock;
#ifdef CONFIG_HAVE_KVM_IRQCHIP
+ /* Update side is protected by irq_lock and,
+ * if configured, irqfds.lock. */
struct kvm_irq_routing_table __rcu *irq_routing;
struct hlist_head mask_notifier_list;
struct hlist_head irq_ack_notifier_list;
@@ -462,6 +465,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
unsigned long *deliver_bitmask);
#endif
int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
+int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
+ int irq_source_id, int level);
void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
void kvm_register_irq_ack_notifier(struct kvm *kvm,
struct kvm_irq_ack_notifier *kian);
@@ -603,6 +608,7 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {}
void kvm_eventfd_init(struct kvm *kvm);
int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags);
void kvm_irqfd_release(struct kvm *kvm);
+void kvm_irq_routing_update(struct kvm *, struct kvm_irq_routing_table *);
int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args);
#else
@@ -614,6 +620,12 @@ static inline int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
}
static inline void kvm_irqfd_release(struct kvm *kvm) {}
+static inline void kvm_irq_routing_update(struct kvm *kvm,
+ struct kvm_irq_routing_table *irq_rt)
+{
+ rcu_assign_pointer(kvm->irq_routing, irq_rt);
+}
+
static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
return -ENOSYS;
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index c1f1e3c..b0cfae7 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -44,14 +44,19 @@
*/
struct _irqfd {
- struct kvm *kvm;
- struct eventfd_ctx *eventfd;
- int gsi;
- struct list_head list;
- poll_table pt;
- wait_queue_t wait;
- struct work_struct inject;
- struct work_struct shutdown;
+ /* Used for MSI fast-path */
+ struct kvm *kvm;
+ wait_queue_t wait;
+ /* Update side is protected by irqfds.lock */
+ struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
+ /* Used for level IRQ fast-path */
+ int gsi;
+ struct work_struct inject;
+ /* Used for setup/shutdown */
+ struct eventfd_ctx *eventfd;
+ struct list_head list;
+ poll_table pt;
+ struct work_struct shutdown;
};
static struct workqueue_struct *irqfd_cleanup_wq;
@@ -125,10 +130,18 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
unsigned long flags = (unsigned long)key;
+ struct kvm_kernel_irq_routing_entry *irq;
- if (flags & POLLIN)
+ if (flags & POLLIN) {
+ rcu_read_lock();
+ irq = rcu_dereference(irqfd->irq_entry);
/* An event has been signaled, inject an interrupt */
- schedule_work(&irqfd->inject);
+ if (irq)
+ kvm_set_msi(irq, irqfd->kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
+ else
+ schedule_work(&irqfd->inject);
+ rcu_read_unlock();
+ }
if (flags & POLLHUP) {
/* The eventfd is closing, detach from KVM */
@@ -163,9 +176,31 @@ irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
add_wait_queue(wqh, &irqfd->wait);
}
+/* Must be called under irqfds.lock */
+static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
+ struct kvm_irq_routing_table *irq_rt)
+{
+ struct kvm_kernel_irq_routing_entry *e;
+ struct hlist_node *n;
+
+ if (irqfd->gsi >= irq_rt->nr_rt_entries) {
+ rcu_assign_pointer(irqfd->irq_entry, NULL);
+ return;
+ }
+
+ hlist_for_each_entry(e, n, &irq_rt->map[irqfd->gsi], link) {
+ /* Only fast-path MSI. */
+ if (e->type == KVM_IRQ_ROUTING_MSI)
+ rcu_assign_pointer(irqfd->irq_entry, e);
+ else
+ rcu_assign_pointer(irqfd->irq_entry, NULL);
+ }
+}
+
static int
kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
{
+ struct kvm_irq_routing_table *irq_rt;
struct _irqfd *irqfd, *tmp;
struct file *file = NULL;
struct eventfd_ctx *eventfd = NULL;
@@ -215,6 +250,10 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
goto fail;
}
+ irq_rt = rcu_dereference_protected(kvm->irq_routing,
+ lockdep_is_held(&kvm->irqfds.lock));
+ irqfd_update(kvm, irqfd, irq_rt);
+
events = file->f_op->poll(file, &irqfd->pt);
list_add_tail(&irqfd->list, &kvm->irqfds.items);
@@ -271,8 +310,15 @@ kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
spin_lock_irq(&kvm->irqfds.lock);
list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
- if (irqfd->eventfd == eventfd && irqfd->gsi == gsi)
+ if (irqfd->eventfd == eventfd && irqfd->gsi == gsi) {
+ /* This rcu_assign_pointer is needed for when
+ * another thread calls kvm_irqfd_update before
+ * we flush workqueue below.
+ * It is paired with synchronize_rcu done by caller
+ * of that function. */
+ rcu_assign_pointer(irqfd->irq_entry, NULL);
irqfd_deactivate(irqfd);
+ }
}
spin_unlock_irq(&kvm->irqfds.lock);
@@ -321,6 +367,23 @@ kvm_irqfd_release(struct kvm *kvm)
}
+/* Change irq_routing and irqfd. Caller must invoke synchronize_rcu
+ * afterwards. */
+void kvm_irq_routing_update(struct kvm *kvm,
+ struct kvm_irq_routing_table *irq_rt)
+{
+ struct _irqfd *irqfd;
+
+ spin_lock_irq(&kvm->irqfds.lock);
+
+ rcu_assign_pointer(kvm->irq_routing, irq_rt);
+
+ list_for_each_entry(irqfd, &kvm->irqfds.items, list)
+ irqfd_update(kvm, irqfd, irq_rt);
+
+ spin_unlock_irq(&kvm->irqfds.lock);
+}
+
/*
* create a host-wide workqueue for issuing deferred shutdown requests
* aggregated from all vm* instances. We need our own isolated single-thread
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 8edca91..9f614b4 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -114,8 +114,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
return r;
}
-static int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
- struct kvm *kvm, int irq_source_id, int level)
+int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
+ struct kvm *kvm, int irq_source_id, int level)
{
struct kvm_lapic_irq irq;
@@ -409,8 +409,9 @@ int kvm_set_irq_routing(struct kvm *kvm,
mutex_lock(&kvm->irq_lock);
old = kvm->irq_routing;
- rcu_assign_pointer(kvm->irq_routing, new);
+ kvm_irq_routing_update(kvm, new);
mutex_unlock(&kvm->irq_lock);
+
synchronize_rcu();
new = old;
--
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