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authorGlauber Costa <glommer@redhat.com>2010-05-11 12:17:47 -0400
committerAvi Kivity <avi@redhat.com>2010-05-19 11:41:07 +0300
commit09c9e81366b9167b88ff05cf29fa94dc3553eb3d (patch)
treeb2555594894cbd5768ee01331fb3a3a7686e6481
parent371bcf646d170ee1325abaf4f3e73485b4fd4d2d (diff)
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KVM: Add cpuid.txt file
This file documents cpuid bits used by KVM. Signed-off-by: Glauber Costa <glommer@redhat.com> Acked-by: Zachary Amsden <zamsden@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
-rw-r--r--Documentation/kvm/cpuid.txt42
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diff --git a/Documentation/kvm/cpuid.txt b/Documentation/kvm/cpuid.txt
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+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 warn if no guest-side
+ || || per-cpu warps are expected in
+ || || kvmclock.
+------------------------------------------------------------------------------