135 lines
4.5 KiB
Diff
135 lines
4.5 KiB
Diff
From: Paul Mackerras <paulus@samba.org>
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Date: Mon, 30 Jun 2014 20:51:09 +1000
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Subject: KVM: Don't keep reference to irq routing table in
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irqfd struct
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Origin: https://git.kernel.org/linus/56f89f3629ffd1a21d38c3d0bea23deac0e284ce
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This makes the irqfd code keep a copy of the irq routing table entry
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for each irqfd, rather than a reference to the copy in the actual
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irq routing table maintained in kvm/virt/irqchip.c. This will enable
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us to change the routing table structure in future, or even not have a
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routing table at all on some platforms.
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The synchronization that was previously achieved using srcu_dereference
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on the read side is now achieved using a seqcount_t structure. That
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ensures that we don't get a halfway-updated copy of the structure if
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we read it while another thread is updating it.
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We still use srcu_read_lock/unlock around the read side so that when
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changing the routing table we can be sure that after calling
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synchronize_srcu, nothing will be using the old routing.
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Signed-off-by: Paul Mackerras <paulus@samba.org>
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Tested-by: Eric Auger <eric.auger@linaro.org>
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Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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virt/kvm/eventfd.c | 41 +++++++++++++++++++++++++----------------
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1 file changed, 25 insertions(+), 16 deletions(-)
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diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
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index 20c3af7..bae593a 100644
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--- a/virt/kvm/eventfd.c
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+++ b/virt/kvm/eventfd.c
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@@ -33,6 +33,7 @@
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#include <linux/kernel.h>
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#include <linux/srcu.h>
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#include <linux/slab.h>
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+#include <linux/seqlock.h>
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#include "iodev.h"
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@@ -75,7 +76,8 @@ struct _irqfd {
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struct kvm *kvm;
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wait_queue_t wait;
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/* Update side is protected by irqfds.lock */
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- struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
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+ struct kvm_kernel_irq_routing_entry irq_entry;
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+ seqcount_t irq_entry_sc;
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/* Used for level IRQ fast-path */
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int gsi;
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struct work_struct inject;
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@@ -223,16 +225,20 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
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{
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struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
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unsigned long flags = (unsigned long)key;
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- struct kvm_kernel_irq_routing_entry *irq;
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+ struct kvm_kernel_irq_routing_entry irq;
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struct kvm *kvm = irqfd->kvm;
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+ unsigned seq;
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int idx;
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if (flags & POLLIN) {
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idx = srcu_read_lock(&kvm->irq_srcu);
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- irq = srcu_dereference(irqfd->irq_entry, &kvm->irq_srcu);
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+ do {
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+ seq = read_seqcount_begin(&irqfd->irq_entry_sc);
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+ irq = irqfd->irq_entry;
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+ } while (read_seqcount_retry(&irqfd->irq_entry_sc, seq));
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/* An event has been signaled, inject an interrupt */
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- if (irq)
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- kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1,
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+ if (irq.type == KVM_IRQ_ROUTING_MSI)
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+ kvm_set_msi(&irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1,
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false);
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else
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schedule_work(&irqfd->inject);
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@@ -277,18 +283,20 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
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{
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struct kvm_kernel_irq_routing_entry *e;
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- if (irqfd->gsi >= irq_rt->nr_rt_entries) {
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- rcu_assign_pointer(irqfd->irq_entry, NULL);
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- return;
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- }
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+ write_seqcount_begin(&irqfd->irq_entry_sc);
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+
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+ irqfd->irq_entry.type = 0;
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+ if (irqfd->gsi >= irq_rt->nr_rt_entries)
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+ goto out;
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hlist_for_each_entry(e, &irq_rt->map[irqfd->gsi], link) {
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/* Only fast-path MSI. */
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if (e->type == KVM_IRQ_ROUTING_MSI)
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- rcu_assign_pointer(irqfd->irq_entry, e);
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- else
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- rcu_assign_pointer(irqfd->irq_entry, NULL);
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+ irqfd->irq_entry = *e;
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}
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+
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+ out:
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+ write_seqcount_end(&irqfd->irq_entry_sc);
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}
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static int
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@@ -310,6 +318,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
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INIT_LIST_HEAD(&irqfd->list);
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INIT_WORK(&irqfd->inject, irqfd_inject);
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INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
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+ seqcount_init(&irqfd->irq_entry_sc);
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f = fdget(args->fd);
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if (!f.file) {
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@@ -466,14 +475,14 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
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list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
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if (irqfd->eventfd == eventfd && irqfd->gsi == args->gsi) {
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/*
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- * This rcu_assign_pointer is needed for when
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+ * This clearing of irq_entry.type is needed for when
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* another thread calls kvm_irq_routing_update before
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* we flush workqueue below (we synchronize with
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* kvm_irq_routing_update using irqfds.lock).
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- * It is paired with synchronize_srcu done by caller
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- * of that function.
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*/
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- rcu_assign_pointer(irqfd->irq_entry, NULL);
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+ write_seqcount_begin(&irqfd->irq_entry_sc);
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+ irqfd->irq_entry.type = 0;
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+ write_seqcount_end(&irqfd->irq_entry_sc);
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irqfd_deactivate(irqfd);
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}
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}
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--
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1.7.10.4
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