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KVM: Don't keep reference to irq routing table in irqfd struct

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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>
This commit is contained in:
Paul Mackerras 2014-06-30 20:51:09 +10:00 committed by Paolo Bonzini
parent 478d668625
commit 56f89f3629
1 changed files with 25 additions and 16 deletions
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41
virt/kvm/eventfd.c
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@ -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);
}
}