PCI 2.3 allows to generically disable IRQ sources at device level. This
enables us to share legacy IRQs of such devices with other host devices
when passing them to a guest.
The new IRQ sharing feature introduced here is optional, user space has
to request it explicitly. Moreover, user space can inform us about its
view of PCI_COMMAND_INTX_DISABLE so that we can avoid unmasking the
interrupt and signaling it if the guest masked it via the virtualized
PCI config space.
Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
---
This applies to kvm/master after merging
PCI: Rework config space blocking services
PCI: Introduce INTx check & mask API
from current linux-next/master. I suppose those two will make it into
3.3.
To recall the history of it: I tried hard to implement an adaptive
solution that automatically picks the fastest masking technique whenever
possible. However, the changes required to the IRQ core subsystem and
the logic of the device assignment code became so complex and partly
ugly that I gave up on this. It's simply not worth the pain given that
legacy PCI interrupts are rarely raised for performance critical device
at such a high rate (KHz...) that you can measure the difference.
Documentation/virtual/kvm/api.txt | 27 +++++
arch/x86/kvm/x86.c | 1 +
include/linux/kvm.h | 6 +
include/linux/kvm_host.h | 2 +
virt/kvm/assigned-dev.c | 208 +++++++++++++++++++++++++++++++-----
5 files changed, 215 insertions(+), 29 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index e1d94bf..670015a 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1159,6 +1159,14 @@ following flags are specified:
/* Depends on KVM_CAP_IOMMU */
#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
+/* The following two depend on KVM_CAP_PCI_2_3 */
+#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
+#define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)
+
+If KVM_DEV_ASSIGN_PCI_2_3 is set, the kernel will manage legacy INTx interrupts
+via the PCI-2.3-compliant device-level mask, thus enable IRQ sharing with other
+assigned devices or host devices. KVM_DEV_ASSIGN_MASK_INTX specifies the
+guest's view on the INTx mask, see KVM_ASSIGN_SET_INTX_MASK for details.
The KVM_DEV_ASSIGN_ENABLE_IOMMU flag is a mandatory option to ensure
isolation of the device. Usages not specifying this flag are deprecated.
@@ -1399,6 +1407,25 @@ The following flags are defined:
If datamatch flag is set, the event will be signaled only if the written value
to the registered address is equal to datamatch in struct kvm_ioeventfd.
+4.59 KVM_ASSIGN_SET_INTX_MASK
+
+Capability: KVM_CAP_PCI_2_3
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_assigned_pci_dev (in)
+Returns: 0 on success, -1 on error
+
+Informs the kernel about the guest's view on the INTx mask. As long as the
+guest masks the legacy INTx, the kernel will refrain from unmasking it at
+hardware level and will not assert the guest's IRQ line. User space is still
+responsible for applying this state to the assigned device's real config space.
+To avoid that the kernel overwrites the state user space wants to set,
+KVM_ASSIGN_SET_INTX_MASK has to be called prior to updating the config space.
+
+See KVM_ASSIGN_DEV_IRQ for the data structure. The target device is specified
+by assigned_dev_id. In the flags field, only KVM_DEV_ASSIGN_MASK_INTX is
+evaluated.
+
4.62 KVM_CREATE_SPAPR_TCE
Capability: KVM_CAP_SPAPR_TCE
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1171def..9381806 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2057,6 +2057,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_XSAVE:
case KVM_CAP_ASYNC_PF:
case KVM_CAP_GET_TSC_KHZ:
+ case KVM_CAP_PCI_2_3:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 68e67e5..da5f7b7 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -556,6 +556,7 @@ struct kvm_ppc_pvinfo {
#define KVM_CAP_PPC_RMA 65
#define KVM_CAP_MAX_VCPUS 66 /* returns max vcpus per vm */
#define KVM_CAP_PPC_PAPR 68
+#define KVM_CAP_PCI_2_3 69
#define KVM_CAP_S390_GMAP 71
#define KVM_CAP_TSC_DEADLINE_TIMER 72
@@ -697,6 +698,9 @@ struct kvm_clock_data {
/* Available with KVM_CAP_TSC_CONTROL */
#define KVM_SET_TSC_KHZ _IO(KVMIO, 0xa2)
#define KVM_GET_TSC_KHZ _IO(KVMIO, 0xa3)
+/* Available with KVM_CAP_PCI_2_3 */
+#define KVM_ASSIGN_SET_INTX_MASK _IOW(KVMIO, 0xa4, \
+ struct kvm_assigned_pci_dev)
/*
* ioctls for vcpu fds
@@ -765,6 +769,8 @@ struct kvm_clock_data {
#define KVM_ALLOCATE_RMA _IOR(KVMIO, 0xa9, struct kvm_allocate_rma)
#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
+#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
+#define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)
struct kvm_assigned_pci_dev {
__u32 assigned_dev_id;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 900c763..07461bd 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -546,6 +546,7 @@ struct kvm_assigned_dev_kernel {
unsigned int entries_nr;
int host_irq;
bool host_irq_disabled;
+ bool pci_2_3;
struct msix_entry *host_msix_entries;
int guest_irq;
struct msix_entry *guest_msix_entries;
@@ -555,6 +556,7 @@ struct kvm_assigned_dev_kernel {
struct pci_dev *dev;
struct kvm *kvm;
spinlock_t intx_lock;
+ struct mutex intx_mask_lock;
char irq_name[32];
struct pci_saved_state *pci_saved_state;
};
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index 758e3b3..b35aba9 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -57,22 +57,66 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
return index;
}
-static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
+static irqreturn_t kvm_assigned_dev_intx(int irq, void *dev_id)
{
struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
+ int ret;
- if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_INTX) {
- spin_lock(&assigned_dev->intx_lock);
+ spin_lock(&assigned_dev->intx_lock);
+ if (pci_check_and_mask_intx(assigned_dev->dev)) {
+ assigned_dev->host_irq_disabled = true;
+ ret = IRQ_WAKE_THREAD;
+ } else
+ ret = IRQ_NONE;
+ spin_unlock(&assigned_dev->intx_lock);
+
+ return ret;
+}
+
+static void
+kvm_assigned_dev_raise_guest_irq(struct kvm_assigned_dev_kernel *assigned_dev,
+ int vector)
+{
+ if (unlikely(assigned_dev->irq_requested_type &
+ KVM_DEV_IRQ_GUEST_INTX)) {
+ mutex_lock(&assigned_dev->intx_mask_lock);
+ if (!(assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX))
+ kvm_set_irq(assigned_dev->kvm,
+ assigned_dev->irq_source_id, vector, 1);
+ mutex_unlock(&assigned_dev->intx_mask_lock);
+ } else
+ kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
+ vector, 1);
+}
+
+static irqreturn_t kvm_assigned_dev_thread_intx(int irq, void *dev_id)
+{
+ struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
+
+ if (!(assigned_dev->flags & KVM_DEV_ASSIGN_PCI_2_3)) {
+ spin_lock_irq(&assigned_dev->intx_lock);
disable_irq_nosync(irq);
assigned_dev->host_irq_disabled = true;
- spin_unlock(&assigned_dev->intx_lock);
+ spin_unlock_irq(&assigned_dev->intx_lock);
}
- kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
- assigned_dev->guest_irq, 1);
+ kvm_assigned_dev_raise_guest_irq(assigned_dev,
+ assigned_dev->guest_irq);
+
+ return IRQ_HANDLED;
+}
+
+#ifdef __KVM_HAVE_MSI
+static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id)
+{
+ struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
+
+ kvm_assigned_dev_raise_guest_irq(assigned_dev,
+ assigned_dev->guest_irq);
return IRQ_HANDLED;
}
+#endif
#ifdef __KVM_HAVE_MSIX
static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
@@ -83,8 +127,7 @@ static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
if (index >= 0) {
vector = assigned_dev->guest_msix_entries[index].vector;
- kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
- vector, 1);
+ kvm_assigned_dev_raise_guest_irq(assigned_dev, vector);
}
return IRQ_HANDLED;
@@ -100,15 +143,31 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
kvm_set_irq(dev->kvm, dev->irq_source_id, dev->guest_irq, 0);
- /* The guest irq may be shared so this ack may be
- * from another device.
- */
- spin_lock(&dev->intx_lock);
- if (dev->host_irq_disabled) {
- enable_irq(dev->host_irq);
- dev->host_irq_disabled = false;
+ mutex_lock(&dev->intx_mask_lock);
+
+ if (!(dev->flags & KVM_DEV_ASSIGN_MASK_INTX)) {
+ bool reassert = false;
+
+ spin_lock_irq(&dev->intx_lock);
+ /*
+ * The guest IRQ may be shared so this ack can come from an
+ * IRQ for another guest device.
+ */
+ if (dev->host_irq_disabled) {
+ if (!(dev->flags & KVM_DEV_ASSIGN_PCI_2_3))
+ enable_irq(dev->host_irq);
+ else if (!pci_check_and_unmask_intx(dev->dev))
+ reassert = true;
+ dev->host_irq_disabled = reassert;
+ }
+ spin_unlock_irq(&dev->intx_lock);
+
+ if (reassert)
+ kvm_set_irq(dev->kvm, dev->irq_source_id,
+ dev->guest_irq, 1);
}
- spin_unlock(&dev->intx_lock);
+
+ mutex_unlock(&dev->intx_mask_lock);
}
static void deassign_guest_irq(struct kvm *kvm,
@@ -156,7 +215,13 @@ static void deassign_host_irq(struct kvm *kvm,
pci_disable_msix(assigned_dev->dev);
} else {
/* Deal with MSI and INTx */
- disable_irq(assigned_dev->host_irq);
+ if (assigned_dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
+ spin_lock_irq(&assigned_dev->intx_lock);
+ pci_intx(assigned_dev->dev, false);
+ spin_unlock_irq(&assigned_dev->intx_lock);
+ synchronize_irq(assigned_dev->host_irq);
+ } else
+ disable_irq(assigned_dev->host_irq);
free_irq(assigned_dev->host_irq, assigned_dev);
@@ -237,15 +302,34 @@ void kvm_free_all_assigned_devices(struct kvm *kvm)
static int assigned_device_enable_host_intx(struct kvm *kvm,
struct kvm_assigned_dev_kernel *dev)
{
+ irq_handler_t irq_handler;
+ unsigned long flags;
+
dev->host_irq = dev->dev->irq;
- /* Even though this is PCI, we don't want to use shared
- * interrupts. Sharing host devices with guest-assigned devices
- * on the same interrupt line is not a happy situation: there
- * are going to be long delays in accepting, acking, etc.
+
+ /*
+ * We can only share the IRQ line with other host devices if we are
+ * able to disable the IRQ source at device-level - independently of
+ * the guest driver. Otherwise host devices may suffer from unbounded
+ * IRQ latencies when the guest keeps the line asserted.
*/
- if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
- IRQF_ONESHOT, dev->irq_name, dev))
+ if (dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
+ irq_handler = kvm_assigned_dev_intx;
+ flags = IRQF_SHARED;
+ } else {
+ irq_handler = NULL;
+ flags = IRQF_ONESHOT;
+ }
+ if (request_threaded_irq(dev->host_irq, irq_handler,
+ kvm_assigned_dev_thread_intx, flags,
+ dev->irq_name, dev))
return -EIO;
+
+ if (dev->flags & KVM_DEV_ASSIGN_PCI_2_3) {
+ spin_lock_irq(&dev->intx_lock);
+ pci_intx(dev->dev, true);
+ spin_unlock_irq(&dev->intx_lock);
+ }
return 0;
}
@@ -262,8 +346,9 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
}
dev->host_irq = dev->dev->irq;
- if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
- 0, dev->irq_name, dev)) {
+ if (request_threaded_irq(dev->host_irq, NULL,
+ kvm_assigned_dev_thread_msi, 0,
+ dev->irq_name, dev)) {
pci_disable_msi(dev->dev);
return -EIO;
}
@@ -321,7 +406,6 @@ static int assigned_device_enable_guest_msi(struct kvm *kvm,
{
dev->guest_irq = irq->guest_irq;
dev->ack_notifier.gsi = -1;
- dev->host_irq_disabled = false;
return 0;
}
#endif
@@ -333,7 +417,6 @@ static int assigned_device_enable_guest_msix(struct kvm *kvm,
{
dev->guest_irq = irq->guest_irq;
dev->ack_notifier.gsi = -1;
- dev->host_irq_disabled = false;
return 0;
}
#endif
@@ -367,6 +450,7 @@ static int assign_host_irq(struct kvm *kvm,
default:
r = -EINVAL;
}
+ dev->host_irq_disabled = false;
if (!r)
dev->irq_requested_type |= host_irq_type;
@@ -468,6 +552,7 @@ static int kvm_vm_ioctl_deassign_dev_irq(struct kvm *kvm,
{
int r = -ENODEV;
struct kvm_assigned_dev_kernel *match;
+ unsigned long irq_type;
mutex_lock(&kvm->lock);
@@ -476,7 +561,9 @@ static int kvm_vm_ioctl_deassign_dev_irq(struct kvm *kvm,
if (!match)
goto out;
- r = kvm_deassign_irq(kvm, match, assigned_irq->flags);
+ irq_type = assigned_irq->flags & (KVM_DEV_IRQ_HOST_MASK |
+ KVM_DEV_IRQ_GUEST_MASK);
+ r = kvm_deassign_irq(kvm, match, irq_type);
out:
mutex_unlock(&kvm->lock);
return r;
@@ -609,6 +696,10 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
if (!match->pci_saved_state)
printk(KERN_DEBUG "%s: Couldn't store %s saved state\n",
__func__, dev_name(&dev->dev));
+
+ if (!pci_intx_mask_supported(dev))
+ assigned_dev->flags &= ~KVM_DEV_ASSIGN_PCI_2_3;
+
match->assigned_dev_id = assigned_dev->assigned_dev_id;
match->host_segnr = assigned_dev->segnr;
match->host_busnr = assigned_dev->busnr;
@@ -616,6 +707,7 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
match->flags = assigned_dev->flags;
match->dev = dev;
spin_lock_init(&match->intx_lock);
+ mutex_init(&match->intx_mask_lock);
match->irq_source_id = -1;
match->kvm = kvm;
match->ack_notifier.irq_acked = kvm_assigned_dev_ack_irq;
@@ -761,6 +853,56 @@ msix_entry_out:
}
#endif
+static int kvm_vm_ioctl_set_pci_irq_mask(struct kvm *kvm,
+ struct kvm_assigned_pci_dev *assigned_dev)
+{
+ int r = 0;
+ struct kvm_assigned_dev_kernel *match;
+
+ mutex_lock(&kvm->lock);
+
+ match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
+ assigned_dev->assigned_dev_id);
+ if (!match) {
+ r = -ENODEV;
+ goto out;
+ }
+
+ mutex_lock(&match->intx_mask_lock);
+
+ match->flags &= ~KVM_DEV_ASSIGN_MASK_INTX;
+ match->flags |= assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX;
+
+ if (match->irq_requested_type & KVM_DEV_IRQ_GUEST_INTX) {
+ if (assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX) {
+ kvm_set_irq(match->kvm, match->irq_source_id,
+ match->guest_irq, 0);
+ /*
+ * Masking at hardware-level is performed on demand,
+ * i.e. when an IRQ actually arrives at the host.
+ */
+ } else {
+ /*
+ * Unmask the IRQ line. It may have been masked
+ * meanwhile if we aren't using PCI 2.3 INTx masking
+ * on the host side.
+ */
+ spin_lock_irq(&match->intx_lock);
+ if (match->host_irq_disabled) {
+ enable_irq(match->host_irq);
+ match->host_irq_disabled = false;
+ }
+ spin_unlock_irq(&match->intx_lock);
+ }
+ }
+
+ mutex_unlock(&match->intx_mask_lock);
+
+out:
+ mutex_unlock(&kvm->lock);
+ return r;
+}
+
long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
unsigned long arg)
{
@@ -868,6 +1010,15 @@ long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
break;
}
#endif
+ case KVM_ASSIGN_SET_INTX_MASK: {
+ struct kvm_assigned_pci_dev assigned_dev;
+
+ r = -EFAULT;
+ if (copy_from_user(&assigned_dev, argp, sizeof assigned_dev))
+ goto out;
+ r = kvm_vm_ioctl_set_pci_irq_mask(kvm, &assigned_dev);
+ break;
+ }
default:
r = -ENOTTY;
break;
@@ -875,4 +1026,3 @@ long kvm_vm_ioctl_assigned_device(struct kvm *kvm, unsigned ioctl,
out:
return r;
}
-
--
1.7.3.4
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