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KVM: Switch assigned device IRQ forwarding to threaded handler
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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 <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Jan Kiszka <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
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@jan-kiszka @avikivity
jan-kiszka authored and avikivity committed Jan 12, 2011
1 parent 0c106b5 commit 0645211
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Showing 2 changed files with 36 additions and 83 deletions.
12 changes: 2 additions & 10 deletions include/linux/kvm_host.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -470,16 +470,8 @@ 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;
Expand All @@ -490,13 +482,13 @@ 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 {
Expand Down
107 changes: 34 additions & 73 deletions virt/kvm/assigned-dev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -55,66 +55,38 @@ 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;
}

/* Ack the irq line for an assigned device */
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;
Expand All @@ -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,
Expand All @@ -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,
Expand All @@ -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);

Expand Down Expand Up @@ -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;
}
Expand All @@ -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;
}
Expand All @@ -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;
}
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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;
Expand Down

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