Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Linux KVM Hypercall: 2 =================== 3 X86: 4 KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall 5 instruction. The hypervisor can replace it with instructions that are 6 guaranteed to be supported. 7 8 Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively. 9 The hypercall number should be placed in rax and the return value will be 10 placed in rax. No other registers will be clobbered unless explicitly stated 11 by the particular hypercall. 12 13 S390: 14 R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall 15 number. The return value is written to R2. 16 17 S390 uses diagnose instruction as hypercall (0x500) along with hypercall 18 number in R1. 19 20 For further information on the S390 diagnose call as supported by KVM, 21 refer to Documentation/virtual/kvm/s390-diag.txt. 22 23 PowerPC: 24 It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers. 25 Return value is placed in R3. 26 27 KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions' 28 property inside the device tree's /hypervisor node. 29 For more information refer to Documentation/virtual/kvm/ppc-pv.txt 30 31 MIPS: 32 KVM hypercalls use the HYPCALL instruction with code 0 and the hypercall 33 number in $2 (v0). Up to four arguments may be placed in $4-$7 (a0-a3) and 34 the return value is placed in $2 (v0). 35 36 KVM Hypercalls Documentation 37 =========================== 38 The template for each hypercall is: 39 1. Hypercall name. 40 2. Architecture(s) 41 3. Status (deprecated, obsolete, active) 42 4. Purpose 43 44 1. KVM_HC_VAPIC_POLL_IRQ 45 ------------------------ 46 Architecture: x86 47 Status: active 48 Purpose: Trigger guest exit so that the host can check for pending 49 interrupts on reentry. 50 51 2. KVM_HC_MMU_OP 52 ------------------------ 53 Architecture: x86 54 Status: deprecated. 55 Purpose: Support MMU operations such as writing to PTE, 56 flushing TLB, release PT. 57 58 3. KVM_HC_FEATURES 59 ------------------------ 60 Architecture: PPC 61 Status: active 62 Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid 63 used to enumerate which hypercalls are available. On PPC, either device tree 64 based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration 65 mechanism (which is this hypercall) can be used. 66 67 4. KVM_HC_PPC_MAP_MAGIC_PAGE 68 ------------------------ 69 Architecture: PPC 70 Status: active 71 Purpose: To enable communication between the hypervisor and guest there is a 72 shared page that contains parts of supervisor visible register state. 73 The guest can map this shared page to access its supervisor register through 74 memory using this hypercall. 75 76 5. KVM_HC_KICK_CPU 77 ------------------------ 78 Architecture: x86 79 Status: active 80 Purpose: Hypercall used to wakeup a vcpu from HLT state 81 Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest 82 kernel mode for an event to occur (ex: a spinlock to become available) can 83 execute HLT instruction once it has busy-waited for more than a threshold 84 time-interval. Execution of HLT instruction would cause the hypervisor to put 85 the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the 86 same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall, 87 specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0) 88 is used in the hypercall for future use. 89 90 91 6. KVM_HC_CLOCK_PAIRING 92 ------------------------ 93 Architecture: x86 94 Status: active 95 Purpose: Hypercall used to synchronize host and guest clocks. 96 Usage: 97 98 a0: guest physical address where host copies 99 "struct kvm_clock_offset" structure. 100 101 a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0) 102 is supported (corresponding to the host's CLOCK_REALTIME clock). 103 104 struct kvm_clock_pairing { 105 __s64 sec; 106 __s64 nsec; 107 __u64 tsc; 108 __u32 flags; 109 __u32 pad[9]; 110 }; 111 112 Where: 113 * sec: seconds from clock_type clock. 114 * nsec: nanoseconds from clock_type clock. 115 * tsc: guest TSC value used to calculate sec/nsec pair 116 * flags: flags, unused (0) at the moment. 117 118 The hypercall lets a guest compute a precise timestamp across 119 host and guest. The guest can use the returned TSC value to 120 compute the CLOCK_REALTIME for its clock, at the same instant. 121 122 Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource, 123 or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.