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KVM: Don't automatically expose the TSC deadline timer in cpuid

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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 <[email protected]>
Tested-by: Alexey Zaytsev <[email protected]>
Signed-off-by: Jan Kiszka <[email protected]>
Signed-off-by: Avi Kivity <[email protected]>
This commit is contained in:
Jan Kiszka 2011-12-21 12:28:29 +01:00 • committed by Avi Kivity
commit 4d25a066b6
3 changed files with 19 additions and 10 deletions
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9
Documentation/virtual/kvm/api.txt
View file

@ -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