193 lines
6.2 KiB
ReStructuredText
193 lines
6.2 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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===================
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Linux KVM Hypercall
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===================
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X86:
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KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
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instruction. The hypervisor can replace it with instructions that are
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guaranteed to be supported.
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Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
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The hypercall number should be placed in rax and the return value will be
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placed in rax. No other registers will be clobbered unless explicitly stated
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by the particular hypercall.
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S390:
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R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
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number. The return value is written to R2.
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S390 uses diagnose instruction as hypercall (0x500) along with hypercall
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number in R1.
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For further information on the S390 diagnose call as supported by KVM,
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refer to Documentation/virt/kvm/s390/s390-diag.rst.
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PowerPC:
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It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
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Return value is placed in R3.
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KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
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property inside the device tree's /hypervisor node.
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For more information refer to Documentation/virt/kvm/ppc-pv.rst
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MIPS:
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KVM hypercalls use the HYPCALL instruction with code 0 and the hypercall
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number in $2 (v0). Up to four arguments may be placed in $4-$7 (a0-a3) and
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the return value is placed in $2 (v0).
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KVM Hypercalls Documentation
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============================
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The template for each hypercall is:
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1. Hypercall name.
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2. Architecture(s)
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3. Status (deprecated, obsolete, active)
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4. Purpose
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1. KVM_HC_VAPIC_POLL_IRQ
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------------------------
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:Architecture: x86
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:Status: active
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:Purpose: Trigger guest exit so that the host can check for pending
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interrupts on reentry.
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2. KVM_HC_MMU_OP
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----------------
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:Architecture: x86
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:Status: deprecated.
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:Purpose: Support MMU operations such as writing to PTE,
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flushing TLB, release PT.
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3. KVM_HC_FEATURES
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------------------
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:Architecture: PPC
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:Status: active
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:Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
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used to enumerate which hypercalls are available. On PPC, either
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device tree based lookup ( which is also what EPAPR dictates)
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OR KVM specific enumeration mechanism (which is this hypercall)
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can be used.
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4. KVM_HC_PPC_MAP_MAGIC_PAGE
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----------------------------
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:Architecture: PPC
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:Status: active
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:Purpose: To enable communication between the hypervisor and guest there is a
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shared page that contains parts of supervisor visible register state.
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The guest can map this shared page to access its supervisor register
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through memory using this hypercall.
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5. KVM_HC_KICK_CPU
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------------------
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:Architecture: x86
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:Status: active
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:Purpose: Hypercall used to wakeup a vcpu from HLT state
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:Usage example:
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A vcpu of a paravirtualized guest that is busywaiting in guest
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kernel mode for an event to occur (ex: a spinlock to become available) can
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execute HLT instruction once it has busy-waited for more than a threshold
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time-interval. Execution of HLT instruction would cause the hypervisor to put
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the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
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same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
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specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
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is used in the hypercall for future use.
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6. KVM_HC_CLOCK_PAIRING
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-----------------------
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:Architecture: x86
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:Status: active
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:Purpose: Hypercall used to synchronize host and guest clocks.
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Usage:
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a0: guest physical address where host copies
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"struct kvm_clock_offset" structure.
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a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
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is supported (corresponding to the host's CLOCK_REALTIME clock).
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::
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struct kvm_clock_pairing {
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__s64 sec;
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__s64 nsec;
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__u64 tsc;
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__u32 flags;
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__u32 pad[9];
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};
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Where:
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* sec: seconds from clock_type clock.
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* nsec: nanoseconds from clock_type clock.
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* tsc: guest TSC value used to calculate sec/nsec pair
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* flags: flags, unused (0) at the moment.
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The hypercall lets a guest compute a precise timestamp across
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host and guest. The guest can use the returned TSC value to
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compute the CLOCK_REALTIME for its clock, at the same instant.
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Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
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or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
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6. KVM_HC_SEND_IPI
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------------------
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:Architecture: x86
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:Status: active
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:Purpose: Send IPIs to multiple vCPUs.
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- a0: lower part of the bitmap of destination APIC IDs
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- a1: higher part of the bitmap of destination APIC IDs
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- a2: the lowest APIC ID in bitmap
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- a3: APIC ICR
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The hypercall lets a guest send multicast IPIs, with at most 128
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128 destinations per hypercall in 64-bit mode and 64 vCPUs per
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hypercall in 32-bit mode. The destinations are represented by a
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bitmap contained in the first two arguments (a0 and a1). Bit 0 of
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a0 corresponds to the APIC ID in the third argument (a2), bit 1
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corresponds to the APIC ID a2+1, and so on.
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Returns the number of CPUs to which the IPIs were delivered successfully.
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7. KVM_HC_SCHED_YIELD
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---------------------
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:Architecture: x86
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:Status: active
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:Purpose: Hypercall used to yield if the IPI target vCPU is preempted
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a0: destination APIC ID
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:Usage example: When sending a call-function IPI-many to vCPUs, yield if
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any of the IPI target vCPUs was preempted.
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8. KVM_HC_MAP_GPA_RANGE
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-------------------------
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:Architecture: x86
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:Status: active
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:Purpose: Request KVM to map a GPA range with the specified attributes.
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a0: the guest physical address of the start page
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a1: the number of (4kb) pages (must be contiguous in GPA space)
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a2: attributes
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Where 'attributes' :
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* bits 3:0 - preferred page size encoding 0 = 4kb, 1 = 2mb, 2 = 1gb, etc...
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* bit 4 - plaintext = 0, encrypted = 1
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* bits 63:5 - reserved (must be zero)
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**Implementation note**: this hypercall is implemented in userspace via
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the KVM_CAP_EXIT_HYPERCALL capability. Userspace must enable that capability
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before advertising KVM_FEATURE_HC_MAP_GPA_RANGE in the guest CPUID. In
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addition, if the guest supports KVM_FEATURE_MIGRATION_CONTROL, userspace
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must also set up an MSR filter to process writes to MSR_KVM_MIGRATION_CONTROL.
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