diff options
Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 6cd63a9010fb..4714f282a43e 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -612,6 +612,20 @@ On some architectures it is required that an interrupt controller model has been previously created with KVM_CREATE_IRQCHIP. Note that edge-triggered interrupts require the level to be set to 1 and then back to 0. +On real hardware, interrupt pins can be active-low or active-high. This +does not matter for the level field of struct kvm_irq_level: 1 always +means active (asserted), 0 means inactive (deasserted). + +x86 allows the operating system to program the interrupt polarity +(active-low/active-high) for level-triggered interrupts, and KVM used +to consider the polarity. However, due to bitrot in the handling of +active-low interrupts, the above convention is now valid on x86 too. +This is signaled by KVM_CAP_X86_IOAPIC_POLARITY_IGNORED. Userspace +should not present interrupts to the guest as active-low unless this +capability is present (or unless it is not using the in-kernel irqchip, +of course). + + ARM/arm64 can signal an interrupt either at the CPU level, or at the in-kernel irqchip (GIC), and for in-kernel irqchip can tell the GIC to use PPIs designated for specific cpus. The irq field is interpreted @@ -628,7 +642,7 @@ The irq_type field has the following values: (The irq_id field thus corresponds nicely to the IRQ ID in the ARM GIC specs) -In both cases, level is used to raise/lower the line. +In both cases, level is used to assert/deassert the line. struct kvm_irq_level { union { |