From: Bruce Rogers Date: Wed, 15 Aug 2012 08:49:02 +0000 (+0300) Subject: KVM: x86: apply kvmclock offset to guest wall clock time X-Git-Tag: v3.5.3~6 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0ad5ec517eab8686580de44007d3af1f0e4bf423;p=thirdparty%2Fkernel%2Fstable.git KVM: x86: apply kvmclock offset to guest wall clock time (cherry picked from commit 4b6486659a7defef82ea51b276024b3aa357fefc) 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 Signed-off-by: Bruce Rogers Signed-off-by: Marcelo Tosatti Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index be6d54929fa7d..14c290de7985b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -907,6 +907,10 @@ 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;