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Based on kernel version 2.6.39.1. Page generated on 2011-06-03 13:47 EST.

1	KVM CPUID bits
2	Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
3	=====================================================
4	
5	A guest running on a kvm host, can check some of its features using
6	cpuid. This is not always guaranteed to work, since userspace can
7	mask-out some, or even all KVM-related cpuid features before launching
8	a guest.
9	
10	KVM cpuid functions are:
11	
12	function: KVM_CPUID_SIGNATURE (0x40000000)
13	returns : eax = 0,
14	          ebx = 0x4b4d564b,
15	          ecx = 0x564b4d56,
16	          edx = 0x4d.
17	Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
18	This function queries the presence of KVM cpuid leafs.
19	
20	
21	function: define KVM_CPUID_FEATURES (0x40000001)
22	returns : ebx, ecx, edx = 0
23	          eax = and OR'ed group of (1 << flag), where each flags is:
24	
25	
26	flag                               || value || meaning
27	=============================================================================
28	KVM_FEATURE_CLOCKSOURCE            ||     0 || kvmclock available at msrs
29	                                   ||       || 0x11 and 0x12.
30	------------------------------------------------------------------------------
31	KVM_FEATURE_NOP_IO_DELAY           ||     1 || not necessary to perform delays
32	                                   ||       || on PIO operations.
33	------------------------------------------------------------------------------
34	KVM_FEATURE_MMU_OP                 ||     2 || deprecated.
35	------------------------------------------------------------------------------
36	KVM_FEATURE_CLOCKSOURCE2           ||     3 || kvmclock available at msrs
37	                                   ||       || 0x4b564d00 and 0x4b564d01
38	------------------------------------------------------------------------------
39	KVM_FEATURE_ASYNC_PF               ||     4 || async pf can be enabled by
40	                                   ||       || writing to msr 0x4b564d02
41	------------------------------------------------------------------------------
42	KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
43	                                   ||       || per-cpu warps are expected in
44	                                   ||       || kvmclock.
45	------------------------------------------------------------------------------
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