-Linux KVM Hypercall:
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+Linux KVM Hypercall
===================
+
X86:
KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
instruction. The hypervisor can replace it with instructions that are
For further information on the S390 diagnose call as supported by KVM,
refer to Documentation/virt/kvm/s390-diag.txt.
- PowerPC:
+PowerPC:
It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
Return value is placed in R3.
the return value is placed in $2 (v0).
KVM Hypercalls Documentation
-===========================
+============================
+
The template for each hypercall is:
1. Hypercall name.
2. Architecture(s)
1. KVM_HC_VAPIC_POLL_IRQ
------------------------
-Architecture: x86
-Status: active
-Purpose: Trigger guest exit so that the host can check for pending
-interrupts on reentry.
+
+:Architecture: x86
+:Status: active
+:Purpose: Trigger guest exit so that the host can check for pending
+ interrupts on reentry.
2. KVM_HC_MMU_OP
-------------------------
-Architecture: x86
-Status: deprecated.
-Purpose: Support MMU operations such as writing to PTE,
-flushing TLB, release PT.
+----------------
+
+:Architecture: x86
+:Status: deprecated.
+:Purpose: Support MMU operations such as writing to PTE,
+ flushing TLB, release PT.
3. KVM_HC_FEATURES
-------------------------
-Architecture: PPC
-Status: active
-Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
-used to enumerate which hypercalls are available. On PPC, either device tree
-based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
-mechanism (which is this hypercall) can be used.
+------------------
+
+:Architecture: PPC
+:Status: active
+:Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
+ used to enumerate which hypercalls are available. On PPC, either
+ device tree based lookup ( which is also what EPAPR dictates)
+ OR KVM specific enumeration mechanism (which is this hypercall)
+ can be used.
4. KVM_HC_PPC_MAP_MAGIC_PAGE
-------------------------
-Architecture: PPC
-Status: active
-Purpose: To enable communication between the hypervisor and guest there is a
-shared page that contains parts of supervisor visible register state.
-The guest can map this shared page to access its supervisor register through
-memory using this hypercall.
+----------------------------
+
+:Architecture: PPC
+:Status: active
+:Purpose: To enable communication between the hypervisor and guest there is a
+ shared page that contains parts of supervisor visible register state.
+ The guest can map this shared page to access its supervisor register
+ through memory using this hypercall.
5. KVM_HC_KICK_CPU
-------------------------
-Architecture: x86
-Status: active
-Purpose: Hypercall used to wakeup a vcpu from HLT state
-Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
-kernel mode for an event to occur (ex: a spinlock to become available) can
-execute HLT instruction once it has busy-waited for more than a threshold
-time-interval. Execution of HLT instruction would cause the hypervisor to put
-the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
-same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
-specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
-is used in the hypercall for future use.
+------------------
+
+:Architecture: x86
+:Status: active
+:Purpose: Hypercall used to wakeup a vcpu from HLT state
+:Usage example:
+ A vcpu of a paravirtualized guest that is busywaiting in guest
+ kernel mode for an event to occur (ex: a spinlock to become available) can
+ execute HLT instruction once it has busy-waited for more than a threshold
+ time-interval. Execution of HLT instruction would cause the hypervisor to put
+ the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
+ same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
+ specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
+ is used in the hypercall for future use.
6. KVM_HC_CLOCK_PAIRING
-------------------------
-Architecture: x86
-Status: active
-Purpose: Hypercall used to synchronize host and guest clocks.
+-----------------------
+:Architecture: x86
+:Status: active
+:Purpose: Hypercall used to synchronize host and guest clocks.
+
Usage:
a0: guest physical address where host copies
a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
is supported (corresponding to the host's CLOCK_REALTIME clock).
+ ::
+
struct kvm_clock_pairing {
__s64 sec;
__s64 nsec;
or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
6. KVM_HC_SEND_IPI
-------------------------
-Architecture: x86
-Status: active
-Purpose: Send IPIs to multiple vCPUs.
+------------------
+
+:Architecture: x86
+:Status: active
+:Purpose: Send IPIs to multiple vCPUs.
-a0: lower part of the bitmap of destination APIC IDs
-a1: higher part of the bitmap of destination APIC IDs
-a2: the lowest APIC ID in bitmap
-a3: APIC ICR
+- a0: lower part of the bitmap of destination APIC IDs
+- a1: higher part of the bitmap of destination APIC IDs
+- a2: the lowest APIC ID in bitmap
+- a3: APIC ICR
The hypercall lets a guest send multicast IPIs, with at most 128
128 destinations per hypercall in 64-bit mode and 64 vCPUs per
Returns the number of CPUs to which the IPIs were delivered successfully.
7. KVM_HC_SCHED_YIELD
-------------------------
-Architecture: x86
-Status: active
-Purpose: Hypercall used to yield if the IPI target vCPU is preempted
+---------------------
+
+:Architecture: x86
+:Status: active
+:Purpose: Hypercall used to yield if the IPI target vCPU is preempted
a0: destination APIC ID
-Usage example: When sending a call-function IPI-many to vCPUs, yield if
-any of the IPI target vCPUs was preempted.
+:Usage example: When sending a call-function IPI-many to vCPUs, yield if
+ any of the IPI target vCPUs was preempted.
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