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Date: Thu, 18 Nov 2010 12:57:41 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Avi Kivity <avi@...hat.com>, 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
So the following on top will fix it all.
Any more comments befpre I bundle it up,
test and report?
kvm: fix up msi fastpath
This will be folded into the msi fastpath patch.
Changes:
- simplify irq_entry/irq_routing update rules:
simply to it all under irqfds.lock
- document locking for rcu update side
- rcu_dereference for rcu pointer access
Still compile-tested only.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b6f7047..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;
@@ -605,7 +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_irqfd_update(struct kvm *kvm, struct kvm_irq_routing_table *irq_rt);
+void kvm_irq_routing_update(struct kvm *, struct kvm_irq_routing_table *);
int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args);
#else
@@ -617,7 +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_irqfd_update(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 49c1864..b0cfae7 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -47,6 +47,7 @@ struct _irqfd {
/* 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;
@@ -133,7 +134,7 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
if (flags & POLLIN) {
rcu_read_lock();
- irq = irqfd->irq_entry;
+ irq = rcu_dereference(irqfd->irq_entry);
/* An event has been signaled, inject an interrupt */
if (irq)
kvm_set_msi(irq, irqfd->kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
@@ -175,6 +176,27 @@ 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)
{
@@ -228,9 +250,9 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
goto fail;
}
- rcu_read_lock();
- irqfd_update(kvm, irqfd, rcu_dereference(kvm->irq_routing));
- rcu_read_unlock();
+ 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);
@@ -345,35 +367,17 @@ kvm_irqfd_release(struct kvm *kvm)
}
-/* 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);
- }
-}
-
-/* Update irqfd after a routing change. Caller must invoke synchronize_rcu
+/* Change irq_routing and irqfd. Caller must invoke synchronize_rcu
* afterwards. */
-void kvm_irqfd_update(struct kvm *kvm, struct kvm_irq_routing_table *irq_rt)
+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);
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 265ab72..9f614b4 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -409,8 +409,7 @@ 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_irqfd_update(kvm, new);
+ kvm_irq_routing_update(kvm, new);
mutex_unlock(&kvm->irq_lock);
synchronize_rcu();
--
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