KVM: Switch assigned device IRQ forwarding to threaded handler

This improves the IRQ forwarding for assigned devices: By using the
kernel's threaded IRQ scheme, we can get rid of the latency-prone work
queue and simplify the code in the same run.

Moreover, we no longer have to hold assigned_dev_lock while raising the
guest IRQ, which can be a lenghty operation as we may have to iterate
over all VCPUs. The lock is now only used for synchronizing masking vs.
unmasking of INTx-type IRQs, thus is renames to intx_lock.

Acked-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 34 insertions, 73 deletions

diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index ecc4419fadca..1d77ce16360a 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -55,58 +55,31 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
         return index;
 }
 
-static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
+static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
 {
-        struct kvm_assigned_dev_kernel *assigned_dev;
-        int i;
+        struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
+        u32 vector;
+        int index;
 
-        assigned_dev = container_of(work, struct kvm_assigned_dev_kernel,
-                                    interrupt_work);
+        if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_INTX) {
+                spin_lock(&assigned_dev->intx_lock);
+                disable_irq_nosync(irq);
+                assigned_dev->host_irq_disabled = true;
+                spin_unlock(&assigned_dev->intx_lock);
+        }
 
-        spin_lock_irq(&assigned_dev->assigned_dev_lock);
         if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX) {
-                struct kvm_guest_msix_entry *guest_entries =
-                        assigned_dev->guest_msix_entries;
-                for (i = 0; i < assigned_dev->entries_nr; i++) {
-                        if (!(guest_entries[i].flags &
-                                        KVM_ASSIGNED_MSIX_PENDING))
-                                continue;
-                        guest_entries[i].flags &= ~KVM_ASSIGNED_MSIX_PENDING;
+                index = find_index_from_host_irq(assigned_dev, irq);
+                if (index >= 0) {
+                        vector = assigned_dev->
+                                        guest_msix_entries[index].vector;
                         kvm_set_irq(assigned_dev->kvm,
-                                    assigned_dev->irq_source_id,
-                                    guest_entries[i].vector, 1);
+                                    assigned_dev->irq_source_id, vector, 1);
                 }
         } else
                 kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
                             assigned_dev->guest_irq, 1);
 
-        spin_unlock_irq(&assigned_dev->assigned_dev_lock);
-}
-
-static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
-{
-        unsigned long flags;
-        struct kvm_assigned_dev_kernel *assigned_dev =
-                (struct kvm_assigned_dev_kernel *) dev_id;
-
-        spin_lock_irqsave(&assigned_dev->assigned_dev_lock, flags);
-        if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX) {
-                int index = find_index_from_host_irq(assigned_dev, irq);
-                if (index < 0)
-                        goto out;
-                assigned_dev->guest_msix_entries[index].flags |=
-                        KVM_ASSIGNED_MSIX_PENDING;
-        }
-
-        schedule_work(&assigned_dev->interrupt_work);
-
-        if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_GUEST_INTX) {
-                disable_irq_nosync(irq);
-                assigned_dev->host_irq_disabled = true;
-        }
-
-out:
-        spin_unlock_irqrestore(&assigned_dev->assigned_dev_lock, flags);
         return IRQ_HANDLED;
 }
 
@@ -114,7 +87,6 @@ out:
 static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
 {
         struct kvm_assigned_dev_kernel *dev;
-        unsigned long flags;
 
         if (kian->gsi == -1)
                 return;
@@ -127,12 +99,12 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
         /* The guest irq may be shared so this ack may be
          * from another device.
          */
-        spin_lock_irqsave(&dev->assigned_dev_lock, flags);
+        spin_lock(&dev->intx_lock);
         if (dev->host_irq_disabled) {
                 enable_irq(dev->host_irq);
                 dev->host_irq_disabled = false;
         }
-        spin_unlock_irqrestore(&dev->assigned_dev_lock, flags);
+        spin_unlock(&dev->intx_lock);
 }
 
 static void deassign_guest_irq(struct kvm *kvm,
@@ -155,28 +127,19 @@ static void deassign_host_irq(struct kvm *kvm,
                               struct kvm_assigned_dev_kernel *assigned_dev)
 {
         /*
-         * In kvm_free_device_irq, cancel_work_sync return true if:
-         * 1. work is scheduled, and then cancelled.
-         * 2. work callback is executed.
-         *
-         * The first one ensured that the irq is disabled and no more events
-         * would happen. But for the second one, the irq may be enabled (e.g.
-         * for MSI). So we disable irq here to prevent further events.
+         * We disable irq here to prevent further events.
          *
          * Notice this maybe result in nested disable if the interrupt type is
          * INTx, but it's OK for we are going to free it.
          *
          * If this function is a part of VM destroy, please ensure that till
          * now, the kvm state is still legal for probably we also have to wait
-         * interrupt_work done.
+         * on a currently running IRQ handler.
          */
         if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX) {
                 int i;
                 for (i = 0; i < assigned_dev->entries_nr; i++)
-                        disable_irq_nosync(assigned_dev->
-                                           host_msix_entries[i].vector);
-
-                cancel_work_sync(&assigned_dev->interrupt_work);
+                        disable_irq(assigned_dev->host_msix_entries[i].vector);
 
                 for (i = 0; i < assigned_dev->entries_nr; i++)
                         free_irq(assigned_dev->host_msix_entries[i].vector,
@@ -188,8 +151,7 @@ static void deassign_host_irq(struct kvm *kvm,
                 pci_disable_msix(assigned_dev->dev);
         } else {
                 /* Deal with MSI and INTx */
-                disable_irq_nosync(assigned_dev->host_irq);
-                cancel_work_sync(&assigned_dev->interrupt_work);
+                disable_irq(assigned_dev->host_irq);
 
                 free_irq(assigned_dev->host_irq, (void *)assigned_dev);
 
@@ -268,8 +230,9 @@ static int assigned_device_enable_host_intx(struct kvm *kvm,
          * on the same interrupt line is not a happy situation: there
          * are going to be long delays in accepting, acking, etc.
          */
-        if (request_irq(dev->host_irq, kvm_assigned_dev_intr,
-                        0, "kvm_assigned_intx_device", (void *)dev))
+        if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
+                                 IRQF_ONESHOT, "kvm_assigned_intx_device",
+                                 (void *)dev))
                 return -EIO;
         return 0;
 }
@@ -287,8 +250,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
         }
 
         dev->host_irq = dev->dev->irq;
-        if (request_irq(dev->host_irq, kvm_assigned_dev_intr, 0,
-                        "kvm_assigned_msi_device", (void *)dev)) {
+        if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
+                                 0, "kvm_assigned_msi_device", (void *)dev)) {
                 pci_disable_msi(dev->dev);
                 return -EIO;
         }
@@ -313,10 +276,10 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
                 return r;
 
         for (i = 0; i < dev->entries_nr; i++) {
-                r = request_irq(dev->host_msix_entries[i].vector,
-                                kvm_assigned_dev_intr, 0,
-                                "kvm_assigned_msix_device",
-                                (void *)dev);
+                r = request_threaded_irq(dev->host_msix_entries[i].vector,
+                                         NULL, kvm_assigned_dev_thread,
+                                         0, "kvm_assigned_msix_device",
+                                         (void *)dev);
                 if (r)
                         goto err;
         }
@@ -557,12 +520,10 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
         match->host_devfn = assigned_dev->devfn;
         match->flags = assigned_dev->flags;
         match->dev = dev;
-        spin_lock_init(&match->assigned_dev_lock);
+        spin_lock_init(&match->intx_lock);
         match->irq_source_id = -1;
         match->kvm = kvm;
         match->ack_notifier.irq_acked = kvm_assigned_dev_ack_irq;
-        INIT_WORK(&match->interrupt_work,
-                  kvm_assigned_dev_interrupt_work_handler);
 
         list_add(&match->list, &kvm->arch.assigned_dev_head);
 
@@ -654,9 +615,9 @@ static int kvm_vm_ioctl_set_msix_nr(struct kvm *kvm,
                         r = -ENOMEM;
                         goto msix_nr_out;
                 }
-                adev->guest_msix_entries = kzalloc(
-                                sizeof(struct kvm_guest_msix_entry) *
-                                entry_nr->entry_nr, GFP_KERNEL);
+                adev->guest_msix_entries =
+                        kzalloc(sizeof(struct msix_entry) * entry_nr->entry_nr,
+                                GFP_KERNEL);
                 if (!adev->guest_msix_entries) {
                         kfree(adev->host_msix_entries);
                         r = -ENOMEM;