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authorPaul Mackerras <paulus@samba.org>2014-06-30 20:51:09 +1000
committerChristoffer Dall <christoffer.dall@linaro.org>2014-10-02 17:19:08 +0200
commit74afc9fff6cdb9df6cd6ee43ddd59465f48aed6d (patch)
treee70a379dda28678ccef4c2f2ae5995b298fa8a33 /virt
parentdad44b58644918b98d32ed35f28e919e08b0f896 (diff)
downloadlinux-linaro-stable-74afc9fff6cdb9df6cd6ee43ddd59465f48aed6d.tar.gz
KVM: Don't keep reference to irq routing table in irqfd struct
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@samba.org> Tested-by: Eric Auger <eric.auger@linaro.org> Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> (cherry picked from commit 56f89f3629ffd1a21d38c3d0bea23deac0e284ce) Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/eventfd.c41
1 files changed, 25 insertions, 16 deletions
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index b51c19ffd8fd..16bf26183225 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);
file = eventfd_fget(args->fd);
if (IS_ERR(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);
}
}