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Subject[PATCH 9/9] Add cpuid.txt file
Date
This file documents cpuid bits used by KVM.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
Documentation/kvm/cpuid.txt | 44 +++++++++++++++++++++++++++++++++++++++++++
1 files changed, 44 insertions(+), 0 deletions(-)
create mode 100644 Documentation/kvm/cpuid.txt

diff --git a/Documentation/kvm/cpuid.txt b/Documentation/kvm/cpuid.txt
new file mode 100644
index 0000000..ca1e89f
--- /dev/null
+++ b/Documentation/kvm/cpuid.txt
@@ -0,0 +1,44 @@
+KVM CPUID bits
+Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
+=====================================================
+
+A guest running on a kvm host, can check some of its features using
+cpuid. This is not always guaranteed to work, since userspace can
+mask-out some, or even all KVM-related cpuid features before launching
+a guest.
+
+KVM cpuid functions are:
+
+function: KVM_CPUID_SIGNATURE (0x40000000)
+returns : eax = 0,
+ ebx = 0x4b4d564b,
+ ecx = 0x564b4d56,
+ edx = 0x4d.
+Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
+This function queries the presence of KVM cpuid leafs.
+
+
+function: define KVM_CPUID_FEATURES (0x40000001)
+returns : ebx, ecx, edx = 0
+ eax = and OR'ed group of (1 << flag), where each flags is:
+
+
+flag || value || meaning
+=============================================================================
+KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
+ || || 0x11 and 0x12.
+------------------------------------------------------------------------------
+KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
+ || || on PIO operations.
+------------------------------------------------------------------------------
+KVM_FEATURE_MMU_OP || 2 || deprecated.
+------------------------------------------------------------------------------
+KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
+ || || 0x4b564d00 and 0x4b564d01
+------------------------------------------------------------------------------
+KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will wanr if no guest-side
+ || || per-cpu warps are expected in
+ || || kvmclock.
+------------------------------------------------------------------------------
+
+
--
1.6.2.2


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