projects / mirror_ubuntu-zesty-kernel.git / blame
| Commit | Line | Data |
|---|---|---|
| 09c9e813 GC |
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) | |
| 57c22e5f | 13 | returns : eax = 0x40000001, |
| 09c9e813 GC |
14 | ebx = 0x4b4d564b, |
| 15 | ecx = 0x564b4d56, | |
| 16 | edx = 0x4d. | |
| 17 | Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM". | |
| 57c22e5f MT |
18 | The value in eax corresponds to the maximum cpuid function present in this leaf, |
| 19 | and will be updated if more functions are added in the future. | |
| 20 | Note also that old hosts set eax value to 0x0. This should | |
| 21 | be interpreted as if the value was 0x40000001. | |
| 09c9e813 GC |
22 | This function queries the presence of KVM cpuid leafs. |
| 23 | ||
| 24 | ||
| 25 | function: define KVM_CPUID_FEATURES (0x40000001) | |
| 26 | returns : ebx, ecx, edx = 0 | |
| 27 | eax = and OR'ed group of (1 << flag), where each flags is: | |
| 28 | ||
| 29 | ||
| 30 | flag || value || meaning | |
| 31 | ============================================================================= | |
| 32 | KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs | |
| 33 | || || 0x11 and 0x12. | |
| 34 | ------------------------------------------------------------------------------ | |
| 35 | KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays | |
| 36 | || || on PIO operations. | |
| 37 | ------------------------------------------------------------------------------ | |
| 38 | KVM_FEATURE_MMU_OP || 2 || deprecated. | |
| 39 | ------------------------------------------------------------------------------ | |
| 40 | KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs | |
| 41 | || || 0x4b564d00 and 0x4b564d01 | |
| 42 | ------------------------------------------------------------------------------ | |
| 344d9588 GN |
43 | KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by |
| 44 | || || writing to msr 0x4b564d02 | |
| 45 | ------------------------------------------------------------------------------ | |
| 56aba608 R |
46 | KVM_FEATURE_STEAL_TIME || 5 || steal time can be enabled by |
| 47 | || || writing to msr 0x4b564d03. | |
| 48 | ------------------------------------------------------------------------------ | |
| 49 | KVM_FEATURE_PV_EOI || 6 || paravirtualized end of interrupt | |
| 50 | || || handler can be enabled by writing | |
| 51 | || || to msr 0x4b564d04. | |
| 52 | ------------------------------------------------------------------------------ | |
| 9bc6cbeb R |
53 | KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit |
| 54 | || || before enabling paravirtualized | |
| 55 | || || spinlock support. | |
| 56 | ------------------------------------------------------------------------------ | |
| 09c9e813 GC |
57 | KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side |
| 58 | || || per-cpu warps are expected in | |
| 59 | || || kvmclock. | |
| 60 | ------------------------------------------------------------------------------ |