On 11/08/2010 01:21 PM, Jan Kiszka wrote:
PCI 2.3 allows to generically disable IRQ sources at device level. This enables us to share IRQs of such devices between on the host side when passing them to a guest. This feature 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 PCI config space.
It's a pity this cannot be done transparently. We could detect multiple devices sharing the line, but what about PCI_COMMAND_INTX_DISABLE?
Perhaps we can hook the kernel's handler for this bit?
/* 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. 4.48 KVM_DEASSIGN_PCI_DEVICE @@ -1263,6 +1271,23 @@ struct kvm_assigned_msix_entry { __u16 padding[3]; }; +5.54 KVM_ASSIGN_SET_INTX_MASK
4.54? (54? wow.)
+ +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 if userspace lies?
+ +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. + diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index fe83eb0..7f1627c 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -468,6 +468,7 @@ 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; @@ -477,6 +478,7 @@ 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]; };
I saw no reason this can't be a spinlock, but perhaps I missed something. This would allow us to avoid srcu, which is slightly more expensive than rcu. Since pci 2.3 assigned devices are not a major use case, I'd like not to penalize the mainstream users for this.
This patch undoes some of the niceness of the previous patches, but I have no alternative to suggest.
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