This makes the irqfd code keep a copy of the irq routing table entry
for each irqfd, rather than a reference to the copy in the actual
irq routing table maintained in kvm/virt/irqchip.c. This will enable
us to change the routing table structure in future, or even not have a
routing table at all on some platforms.
The synchronization that was previously achieved using srcu_dereference
on the read side is now achieved using a seqcount_t structure. That
ensures that we don't get a halfway-updated copy of the structure if
we read it while another thread is updating it.
We still use srcu_read_lock/unlock around the read side so that when
changing the routing table we can be sure that after calling
synchronize_srcu, nothing will be using the old routing.
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
---
virt/kvm/eventfd.c | 41 +++++++++++++++++++++++++----------------
1 file changed, 25 insertions(+), 16 deletions(-)
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 20c3af7..bae593a 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -33,6 +33,7 @@
#include <linux/kernel.h>
#include <linux/srcu.h>
#include <linux/slab.h>
+#include <linux/seqlock.h>
#include "iodev.h"
@@ -75,7 +76,8 @@ struct _irqfd {
struct kvm *kvm;
wait_queue_t wait;
/* Update side is protected by irqfds.lock */
- struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
+ struct kvm_kernel_irq_routing_entry irq_entry;
+ seqcount_t irq_entry_sc;
/* Used for level IRQ fast-path */
int gsi;
struct work_struct inject;
@@ -223,16 +225,20 @@ 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;
+ struct kvm_kernel_irq_routing_entry irq;
struct kvm *kvm = irqfd->kvm;
+ unsigned seq;
int idx;
if (flags & POLLIN) {
idx = srcu_read_lock(&kvm->irq_srcu);
- irq = srcu_dereference(irqfd->irq_entry, &kvm->irq_srcu);
+ do {
+ seq = read_seqcount_begin(&irqfd->irq_entry_sc);
+ irq = irqfd->irq_entry;
+ } while (read_seqcount_retry(&irqfd->irq_entry_sc, seq));
/* An event has been signaled, inject an interrupt */
- if (irq)
- kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1,
+ if (irq.type == KVM_IRQ_ROUTING_MSI)
+ kvm_set_msi(&irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1,
false);
else
schedule_work(&irqfd->inject);
@@ -277,18 +283,20 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
{
struct kvm_kernel_irq_routing_entry *e;
- if (irqfd->gsi >= irq_rt->nr_rt_entries) {
- rcu_assign_pointer(irqfd->irq_entry, NULL);
- return;
- }
+ write_seqcount_begin(&irqfd->irq_entry_sc);
+
+ irqfd->irq_entry.type = 0;
+ if (irqfd->gsi >= irq_rt->nr_rt_entries)
+ goto out;
hlist_for_each_entry(e, &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);
+ irqfd->irq_entry = *e;
}
+
+ out:
+ write_seqcount_end(&irqfd->irq_entry_sc);
}
static int
@@ -310,6 +318,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
INIT_LIST_HEAD(&irqfd->list);
INIT_WORK(&irqfd->inject, irqfd_inject);
INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
+ seqcount_init(&irqfd->irq_entry_sc);
f = fdget(args->fd);
if (!f.file) {
@@ -466,14 +475,14 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi) {
/*
- * This rcu_assign_pointer is needed for when
+ * This clearing of irq_entry.type is needed for when
* another thread calls kvm_irq_routing_update before
* we flush workqueue below (we synchronize with
* kvm_irq_routing_update using irqfds.lock).
- * It is paired with synchronize_srcu done by caller
- * of that function.
*/
- rcu_assign_pointer(irqfd->irq_entry, NULL);
+ write_seqcount_begin(&irqfd->irq_entry_sc);
+ irqfd->irq_entry.type = 0;
+ write_seqcount_end(&irqfd->irq_entry_sc);
irqfd_deactivate(irqfd);
}
}
--
2.0.0
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