This patchset implements the KVM part of the synthetic interrupt
controller (SynIC) which is a building block of the Hyper-V
paravirtualized device bus (vmbus).

SynIC is a lapic extension, which is controlled via MSRs and maintains
for each vCPU
 - 16 synthetic interrupt "lines" (SINT's); each can be configured to
   trigger a specific interrupt vector optionally with auto-EOI
 - a message page in the guest memory with 16 256-byte per-SINT message
 - an event flag page in the guest memory with 16 2048-bit per-SINT
   event flag areas

The host triggers a SINT whenever it delivers a new message to the
corresponding slot or flips an event flag bit in the corresponding area.
The guest informs the host that it can try delivering a message by
explicitly asserting EOI in lapic or writing to End-Of-Message (EOM)

The userspace (qemu) triggers interrupts and receives EOM notifications
via irqfd with resampler; for that, a GSI is allocated for each
configured SINT, and irq_routing api is extended to support GSI-SINT

Besides, a new vcpu exit is introduced to notify the userspace of the
changes in SynIC configuraion triggered by guest writing to the
corresponding MSRs.

Signed-off-by: Andrey Smetanin <>
Reviewed-by: Roman Kagan <>
Signed-off-by: Denis V. Lunev <>
CC: Vitaly Kuznetsov <>
CC: "K. Y. Srinivasan" <>
CC: Gleb Natapov <>
CC: Paolo Bonzini <>

Changes v2:
* irqchip/eventfd preparation improvements to support
  arch specific routing entries like Hyper-V SynIC ones.
* add Hyper-V SynIC vectors into EOI exit bitmap.
* do not use posted interrupts in case of Hyper-V SynIC
  AutoEOI vectors

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