linux/Documentation/virtual/kvm
Jan Kiszka 4d25a066b6 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>
2011-12-26 13:27:44 +02:00
..
api.txt KVM: Don't automatically expose the TSC deadline timer in cpuid 2011-12-26 13:27:44 +02:00
cpuid.txt
locking.txt
mmu.txt KVM: MMU: Adjust shadow paging to work when SMEP=1 and CR0.WP=0 2011-07-12 13:16:26 +03:00
msr.txt KVM: KVM Steal time guest/host interface 2011-07-12 13:17:03 +03:00
nested-vmx.txt KVM: nVMX: Documentation 2011-07-12 13:15:22 +03:00
ppc-pv.txt KVM: PPC: e500: enable magic page 2011-07-12 13:16:37 +03:00
review-checklist.txt Correct occurrences of 2011-05-06 09:27:55 -07:00
timekeeping.txt