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authorJan Kiszka <jan.kiszka@siemens.com>2011-12-21 12:28:29 +0100
committerAvi Kivity <avi@redhat.com>2011-12-26 13:27:44 +0200
commit4d25a066b69fb749a39d0d4c610689dd765a0b0e (patch)
tree34f644f5a0f734a815225cade757088a9862318b /Documentation/virtual
parent3d27e23b17010c668db311140b17bbbb70c78fb9 (diff)
KVM: Don't automatically expose the TSC deadline timer in cpuid
Unlike all of the other cpuid bits, the TSC deadline timer bit is set unconditionally, regardless of what userspace wants. This is broken in several ways: - if userspace doesn't use KVM_CREATE_IRQCHIP, and doesn't emulate the TSC deadline timer feature, a guest that uses the feature will break - live migration to older host kernels that don't support the TSC deadline timer will cause the feature to be pulled from under the guest's feet; breaking it - guests that are broken wrt the feature will fail. Fix by not enabling the feature automatically; instead report it to userspace. Because the feature depends on KVM_CREATE_IRQCHIP, which we cannot guarantee will be called, we expose it via a KVM_CAP_TSC_DEADLINE_TIMER and not KVM_GET_SUPPORTED_CPUID. Fixes the Illumos guest kernel, which uses the TSC deadline timer feature. [avi: add the KVM_CAP + documentation] Reported-by: Alexey Zaytsev <alexey.zaytsev@gmail.com> Tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'Documentation/virtual')
-rw-r--r--Documentation/virtual/kvm/api.txt9
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 4df9af4f6132..e2a4b5287361 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1100,6 +1100,15 @@ emulate them efficiently. The fields in each entry are defined as follows:
eax, ebx, ecx, edx: the values returned by the cpuid instruction for
this function/index combination
+The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned
+as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC
+support. Instead it is reported via
+
+ ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER)
+
+if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the
+feature in userspace, then you can enable the feature for KVM_SET_CPUID2.
+
4.47 KVM_PPC_GET_PVINFO
Capability: KVM_CAP_PPC_GET_PVINFO