KVM: Don't automatically expose the TSC deadline timer in cpuid
authorJan Kiszka <jan.kiszka@siemens.com>
Wed, 21 Dec 2011 11:28:29 +0000 (12:28 +0100)
committerAvi Kivity <avi@redhat.com>
Mon, 26 Dec 2011 11:27:44 +0000 (13:27 +0200)
commit4d25a066b69fb749a39d0d4c610689dd765a0b0e
tree34f644f5a0f734a815225cade757088a9862318b
parent3d27e23b17010c668db311140b17bbbb70c78fb9
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>
Documentation/virtual/kvm/api.txt
arch/x86/kvm/x86.c
include/linux/kvm.h