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    SubjectRe: [PATCH 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices
    On 12/04/2010 01:37 AM, Jan Kiszka wrote:
    > From: Jan Kiszka<jan.kiszka@siemens.com>
    >
    > PCI 2.3 allows to generically disable IRQ sources at device level. This
    > enables us to share IRQs of such devices on the host side when passing
    > them to a guest.
    >
    > However, IRQ disabling via the PCI config space is more costly than
    > masking the line via disable_irq. Therefore we register an IRQ sharing
    > notifier and switch between line and device level disabling on demand.
    >
    > This feature is optional, user space has to request it explicitly as it
    > also has to inform us about its view of PCI_COMMAND_INTX_DISABLE. That
    > way, we can avoid unmasking the interrupt and signaling it if the guest
    > masked it via the PCI config space.
    >
    >
    > diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
    > index e1a9297..5e164db 100644
    > --- a/Documentation/kvm/api.txt
    > +++ b/Documentation/kvm/api.txt
    > @@ -1112,6 +1112,14 @@ 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, but only if IRQ sharing with other
    > +assigned or host devices requires it. KVM_DEV_ASSIGN_MASK_INTX specifies the
    > +guest's view on the INTx mask, see KVM_ASSIGN_SET_INTX_MASK for details.
    >
    > 4.48 KVM_DEASSIGN_PCI_DEVICE
    >
    > @@ -1263,6 +1271,23 @@ struct kvm_assigned_msix_entry {
    > __u16 padding[3];
    > };
    >
    > +4.54 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.

    What's the protocol for doing this? I suppose userspace has to disable
    interrupts, ioctl(SET_INTX_MASK, masked), ..., ioctl(SET_INTX_MASK,
    unmasked), enable interrupts?

    Isn't there a race window between the two operations?

    Maybe we should give the kernel full ownership of that bit.

    > +
    > +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.
    > +

    --
    error compiling committee.c: too many arguments to function



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