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When guest time is reset with KVM_SET_CLOCK(0), it is possible for 'hv_clock->system_time' to become a small negative number. This happens because in KVM_SET_CLOCK handling we set 'kvm->arch.kvmclock_offset' based on get_kvmclock_ns(kvm) but when KVM_REQ_CLOCK_UPDATE is handled, kvm_guest_time_update() does (masterclock in use case): hv_clock.system_time = ka->master_kernel_ns + v->kvm->arch.kvmclock_offset; And 'master_kernel_ns' represents the last time when masterclock got updated, it can precede KVM_SET_CLOCK() call. Normally, this is not a problem, the difference is very small, e.g. I'm observing hv_clock.system_time = -70 ns. The issue comes from the fact that 'hv_clock.system_time' is stored as unsigned and 'system_time / 100' in compute_tsc_page_parameters() becomes a very big number. Use 'master_kernel_ns' instead of get_kvmclock_ns() when masterclock is in use and get_kvmclock_base_ns() when it's not to prevent 'system_time' from going negative. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Message-Id: <20210331124130.337992-2-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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