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KVM: arm/arm64: Add ARM user space interrupt signaling ABI

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We have 2 modes for dealing with interrupts in the ARM world. We can
either handle them all using hardware acceleration through the vgic or
we can emulate a gic in user space and only drive CPU IRQ pins from
there.

Unfortunately, when driving IRQs from user space, we never tell user
space about events from devices emulated inside the kernel, which may
result in interrupt line state changes, so we lose out on for example
timer and PMU events if we run with user space gic emulation.

Define an ABI to publish such device output levels to userspace.

Reviewed-by: Alexander Graf <[email protected]>
Reviewed-by: Marc Zyngier <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>
Signed-off-by: Christoffer Dall <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
This commit is contained in:
Alexander Graf 2016-09-27 21:08:05 +02:00 • committed by Christoffer Dall
commit 3fe17e6826
4 changed files with 54 additions and 0 deletions
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42
Documentation/virtual/kvm/api.txt
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@ -4147,3 +4147,45 @@ This capability, if KVM_CHECK_EXTENSION indicates that it is
available, means that that the kernel can support guests using the
hashed page table MMU defined in Power ISA V3.00 (as implemented in
the POWER9 processor), including in-memory segment tables.
8.5 KVM_CAP_ARM_USER_IRQ
Architectures: arm, arm64
This capability, if KVM_CHECK_EXTENSION indicates that it is available, means
that if userspace creates a VM without an in-kernel interrupt controller, it
will be notified of changes to the output level of in-kernel emulated devices,
which can generate virtual interrupts, presented to the VM.
For such VMs, on every return to userspace, the kernel
updates the vcpu's run->s.regs.device_irq_level field to represent the actual
output level of the device.
Whenever kvm detects a change in the device output level, kvm guarantees at
least one return to userspace before running the VM. This exit could either
be a KVM_EXIT_INTR or any other exit event, like KVM_EXIT_MMIO. This way,
userspace can always sample the device output level and re-compute the state of
the userspace interrupt controller. Userspace should always check the state
of run->s.regs.device_irq_level on every kvm exit.
The value in run->s.regs.device_irq_level can represent both level and edge
triggered interrupt signals, depending on the device. Edge triggered interrupt
signals will exit to userspace with the bit in run->s.regs.device_irq_level
set exactly once per edge signal.
The field run->s.regs.device_irq_level is available independent of
run->kvm_valid_regs or run->kvm_dirty_regs bits.
If KVM_CAP_ARM_USER_IRQ is supported, the KVM_CHECK_EXTENSION ioctl returns a
number larger than 0 indicating the version of this capability is implemented
and thereby which bits in in run->s.regs.device_irq_level can signal values.
Currently the following bits are defined for the device_irq_level bitmap:
KVM_CAP_ARM_USER_IRQ >= 1:
KVM_ARM_DEV_EL1_VTIMER - EL1 virtual timer
KVM_ARM_DEV_EL1_PTIMER - EL1 physical timer
KVM_ARM_DEV_PMU - ARM PMU overflow interrupt signal
Future versions of kvm may implement additional events. These will get
indicated by returning a higher number from KVM_CHECK_EXTENSION and will be
listed above.