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KVM: x86: apply kvmclock offset to guest wall clock time 

When a guest migrates to a new host, the system time difference from the
previous host is used in the updates to the kvmclock system time visible
to the guest, resulting in a continuation of correct kvmclock based guest
timekeeping.

The wall clock component of the kvmclock provided time is currently not
updated with this same time offset. Since the Linux guest caches the
wall clock based time, this discrepency is not noticed until the guest is
rebooted. After reboot the guest's time calculations are off.

This patch adjusts the wall clock by the kvmclock_offset, resulting in
correct guest time after a reboot.

Cc: Zachary Amsden <zamsden@gmail.com>
Signed-off-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Bruce Rogers 2012-07-20 10:44:24 -06:00 committed by Marcelo Tosatti
parent aea218f3cb
commit 4b6486659a
1 changed files with 4 additions and 0 deletions
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4
arch/x86/kvm/x86.c
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@ -925,6 +925,10 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
*/
getboottime(&boot);
if (kvm->arch.kvmclock_offset) {
struct timespec ts = ns_to_timespec(kvm->arch.kvmclock_offset);
boot = timespec_sub(boot, ts);
}
wc.sec = boot.tv_sec;
wc.nsec = boot.tv_nsec;
wc.version = version;