[PATCH v4 4/9] KVM: Switch assigned device IRQ forwarding to threaded handler

Jan Kiszka
2010-11-08T11:22:11Z

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.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
include/linux/kvm_host.h | 12 +----
virt/kvm/assigned-dev.c | 107 +++++++++++++++-------------------------------
2 files changed, 36 insertions(+), 83 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 83bf8e1..050674f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -458,16 +458,8 @@ struct kvm_irq_ack_notifier {
void (*irq_acked)(struct kvm_irq_ack_notifier *kian);
};

-#define KVM_ASSIGNED_MSIX_PENDING 0x1
-struct kvm_guest_msix_entry {
- u32 vector;
- u16 entry;
- u16 flags;
-};
-
struct kvm_assigned_dev_kernel {
struct kvm_irq_ack_notifier ack_notifier;
- struct work_struct interrupt_work;
struct list_head list;
int assigned_dev_id;
int host_segnr;
@@ -478,13 +470,13 @@ struct kvm_assigned_dev_kernel {
bool host_irq_disabled;
struct msix_entry *host_msix_entries;
int guest_irq;
- struct kvm_guest_msix_entry *guest_msix_entries;
+ struct msix_entry *guest_msix_entries;
unsigned long irq_requested_type;
int irq_source_id;
int flags;
struct pci_dev *dev;
struct kvm *kvm;
- spinlock_t assigned_dev_lock;
+ spinlock_t intx_lock;
};

struct kvm_irq_mask_notifier {
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index ecc4419..1d77ce1 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;
--
1.7.1