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Documentation / virtual / kvm / hypercalls.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:05 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	 PowerPC:
21	  It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
22	  Return value is placed in R3.
23	
24	  KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
25	  property inside the device tree's /hypervisor node.
26	  For more information refer to Documentation/virtual/kvm/ppc-pv.txt
27	
28	KVM Hypercalls Documentation
29	===========================
30	The template for each hypercall is:
31	1. Hypercall name.
32	2. Architecture(s)
33	3. Status (deprecated, obsolete, active)
34	4. Purpose
35	
36	1. KVM_HC_VAPIC_POLL_IRQ
37	------------------------
38	Architecture: x86
39	Status: active
40	Purpose: Trigger guest exit so that the host can check for pending
41	interrupts on reentry.
42	
43	2. KVM_HC_MMU_OP
44	------------------------
45	Architecture: x86
46	Status: deprecated.
47	Purpose: Support MMU operations such as writing to PTE,
48	flushing TLB, release PT.
49	
50	3. KVM_HC_FEATURES
51	------------------------
52	Architecture: PPC
53	Status: active
54	Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
55	used to enumerate which hypercalls are available. On PPC, either device tree
56	based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
57	mechanism (which is this hypercall) can be used.
58	
59	4. KVM_HC_PPC_MAP_MAGIC_PAGE
60	------------------------
61	Architecture: PPC
62	Status: active
63	Purpose: To enable communication between the hypervisor and guest there is a
64	shared page that contains parts of supervisor visible register state.
65	The guest can map this shared page to access its supervisor register through
66	memory using this hypercall.
67	
68	5. KVM_HC_KICK_CPU
69	------------------------
70	Architecture: x86
71	Status: active
72	Purpose: Hypercall used to wakeup a vcpu from HLT state
73	Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
74	kernel mode for an event to occur (ex: a spinlock to become available) can
75	execute HLT instruction once it has busy-waited for more than a threshold
76	time-interval. Execution of HLT instruction would cause the hypervisor to put
77	the vcpu to sleep until occurence of an appropriate event. Another vcpu of the
78	same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
79	specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
80	is used in the hypercall for future use.
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