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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 <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> |
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