On Mon, 2012-02-27 at 23:07 +0100, Jan Kiszka wrote:
> On 2012-02-27 22:05, Alex Williamson wrote:
> > On Fri, 2012-02-10 at 19:17 +0100, Jan Kiszka wrote:
> >> 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>
> >> ---
> >>
> >> Changes in v3:
> >> - rebased over current kvm.git (no code conflict, just api.txt)
> >>
> >> Documentation/virtual/kvm/api.txt | 31 ++++++
> >> 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, 219 insertions(+), 29 deletions(-)
> >>
> >> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> >> index 59a3826..5ce0e29 100644
> >> --- a/Documentation/virtual/kvm/api.txt
> >> +++ b/Documentation/virtual/kvm/api.txt
> >> @@ -1169,6 +1169,14 @@ 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.
> >> @@ -1441,6 +1449,29 @@ The "num_dirty" field is a performance hint for KVM to determine whether it
> >> should skip processing the bitmap and just invalidate everything. It must
> >> be set to the number of set bits in the bitmap.
> >>
> >> +4.60 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
> >> +by setting or clearing the Interrupt Disable bit 10 in the Command register.
> >> +
> >> +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.
> >> +Moreover, user space has to write back its own view on the Interrupt Disable
> >> +bit whenever modifying the Command word.
> >
> > This is very confusing. I think we need to work on the wording, but
> > perhaps it's not worth hold up the patch. It seems the simplest,
>
> As I need another round anyway (see below), I'm open for better wording
> suggestions.
Now that I know what it does, I'll probably write something just as
confusing, but here's a shot:
Allows userspace to mask PCI INTx interrupts from the assigned
device. The kernel will not deliver INTx interrupts to the
guest between setting and clearing of KVM_ASSIGN_SET_INTX_MASK
via this interface. This enables use of and emulation of PCI
2.3 INTx disable command register behavior.
This may be used for both PCI 2.3 devices supporting INTx
disable natively and older devices lacking this support.
Userspace is responsible for emulating the read value of the
INTx disable bit in the guest visible PCI command register.
When modifying the INTx disable state, userspace should precede
updating the physical device command register by calling this
ioctl to inform the kernel of the new intended INTx mask state.
Note that the kernel uses the device INTx disable bit to
internally manage the device interrupt state for PCI 2.3
devices. Reads of this register may therefore not match the
expected value. Writes should always use the guest intended
INTx disable value rather than attempting to read-copy-update
the current physical device state. Races between user and
kernel updates to the INTx disable bit are handled lazily in the
kernel. It's possible the device may generate unintended
interrupts, but they will not be injected into the guest.
> > un-optimized version of writing to the command register from userspace
> > is then:
> >
> > ioctl(kvm_fd, KVM_ASSIGN_SET_INTX_MASK,
> > .flags = (command & PCI_COMMAND_INTX_DISABLE) ?
> > KVM_DEV_ASSIGN_MASK_INTX : 0);
> > pwrite(config_fd, &command, 2, PCI_COMMAND);
> >
> > From the v1 discussion, I take it that in the case where we're unmasking
> > a pending interrupt, the ioctl will post the interrupt, leaving INTx
> > disable set; the pwrite will clear INTx disable on the device, assuming
> > irq is still pending, trigger the kvm irq handler, which will set INTx
>
> s/set/clear? Yes.
>
> > disable and repost the interrupt. We assume that single spurious
> > interrupts are ok
>
> Spurious for the host, but not visible for the guest at any time (unless
> user space messes it up).
Ok
> > and we also assume that it's the responsibility of
> > userspace to present an emulated INTx disable value on read to avoid
> > confusing guests.
> >
> > More below...
> >
> >> +
> >> +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 2bd77a3..1f11435 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -2099,6 +2099,7 @@ 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 acbe429..6c322a9 100644
> >> --- a/include/linux/kvm.h
> >> +++ b/include/linux/kvm.h
> >> @@ -588,6 +588,7 @@ struct kvm_ppc_pvinfo {
> >> #define KVM_CAP_TSC_DEADLINE_TIMER 72
> >> #define KVM_CAP_S390_UCONTROL 73
> >> #define KVM_CAP_SYNC_REGS 74
> >> +#define KVM_CAP_PCI_2_3 75
> >>
> >> #ifdef KVM_CAP_IRQ_ROUTING
> >>
> >> @@ -784,6 +785,9 @@ struct kvm_s390_ucas_mapping {
> >> /* 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
> >> @@ -857,6 +861,8 @@ struct kvm_s390_ucas_mapping {
> >> #define KVM_SET_ONE_REG _IOW(KVMIO, 0xac, struct kvm_one_reg)
> >>
> >> #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 9698080..d1d68f4 100644
> >> --- a/include/linux/kvm_host.h
> >> +++ b/include/linux/kvm_host.h
> >> @@ -547,6 +547,7 @@ 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;
> >> @@ -556,6 +557,7 @@ 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 ece8061..3ee2970 100644
> >> --- a/virt/kvm/assigned-dev.c
> >> +++ b/virt/kvm/assigned-dev.c
> >> @@ -55,22 +55,66 @@ 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)
> >> @@ -81,8 +125,7 @@ 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;
> >> @@ -98,15 +141,31 @@ 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,
> >> @@ -154,7 +213,13 @@ 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);
> >
> > We're disabling INTx in response to de-assigning MSI here too, is that
> > intended?
>
> Hmm, actually no. We should not take the intx path if the assigned IRQ
> was of MSI kind. Will fix.
Ok
> > I have trouble reading the spec that way, but I know this
> > isn't the first time it's been asserted that INTx disable does both.
> >
> >>
> >> free_irq(assigned_dev->host_irq, assigned_dev);
> >>
> >> @@ -235,15 +300,34 @@ 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);
> >
> > Here we unmask INTx disable when enabling INTx, but we don't do the same
> > below when enabling MSI.
>
> INTx is enabled by default after a device reset which we performed on
> device assignment.
True, we do have a specified reset value of zero.
> >
> > IIRC, we don't treat failure to save/restore PCI state around assignment
> > as fatal, but we rely on it for restoring INTx disable when the device
> > is returned. Is there a small window where we can hand back a device in
> > an unusable state?
>
> How could this state look like? Also on release, we reset the device,
> and this leaves INTx disable cleared behind.
Does being PCI 2.3 guarantee we have a reset mechanism? I don't think
it does. Maybe it's a catch-22; if there's no reset mechanism we could
re-enable INTx before we hand the device back, but if there's no reset
mechanism, can we be sure the device is in a quiesced state that we feel
comfortable re-enabling interrupts. Let's not worry about it.
> >
> >> + }
> >> return 0;
> >> }
> >>
> >> @@ -260,8 +344,9 @@ 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;
> >> }
> >> @@ -319,7 +404,6 @@ 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
> >> @@ -331,7 +415,6 @@ 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
> >> @@ -365,6 +448,7 @@ 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;
> >> @@ -466,6 +550,7 @@ 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);
> >>
> >> @@ -474,7 +559,9 @@ 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;
> >> @@ -607,6 +694,10 @@ 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;
> >> @@ -614,6 +705,7 @@ 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;
> >> @@ -759,6 +851,56 @@ 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);
> >
> > How do we not get an unbalanced enable here for PCI 2.3 devices?
>
> By performing both the disable and the host_irq_disabled update under
> intx_lock? Or which scenario do you see?
Do we ever do disable_irq() on a PCI 2.3 device? Seems like we only use
the intx API for them, and disable/enable_irq exclusively on non-2.3, so
if we can get here on a 2.3 device we have unbalanced enables. Am I
missing some nuance of host_irq_disabled that prevents 2.3 from getting
here? Thanks,
Alex
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