mirror of https://gitee.com/openkylin/linux.git
0bc48bea36
kvm master clock usually has a different frequency than the kernel boot clock. This is not a problem until the master clock is updated; update uses the current kernel boot clock to compute new kvm clock, which erases any kvm clock cycles that might have built up due to frequency difference over a long period. KVM_SET_CLOCK is one of places where we can safely update master clock as the guest-visible clock is going to be shifted anyway. The problem with current code is that it updates the kvm master clock after updating the offset. If the master clock was enabled before calling KVM_SET_CLOCK, then it might have built up a significant delta from kernel boot clock. In the worst case, the time set by userspace would be shifted by so much that it couldn't have been set at any point during KVM_SET_CLOCK. To fix this, move kvm_gen_update_masterclock() before computing kvmclock_offset, which means that the master clock and kernel boot clock will be sufficiently close together. Another solution would be to replace get_kvmclock_ns() with "ktime_get_boot_ns() + ka->kvmclock_offset", which is marginally more accurate, but would break symmetry with KVM_GET_CLOCK. Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> |
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