[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4 3/3] x86/HVM: Use fixed TSC value when saving or restoring domain
>>> On 16.04.14 at 03:27, <boris.ostrovsky@xxxxxxxxxx> wrote: > When a domain is saved each VCPU's TSC value needs to be preserved. To get it > we > use hvm_get_guest_tsc(). This routine (either itself or via get_s_time() > which > it may call) calculates VCPU's TSC based on current host's TSC value (by > doing a > rdtscll()). Since this is performed for each VCPU separately we end up with > un-synchronized TSCs. > > Similarly, during a restore each VCPU is assigned its TSC based on host's > current > tick, causing virtual TSCs to diverge further. > > With this, we can easily get into situation where a guest may see time going > backwards. > > Instead of reading new TSC value for each VCPU when saving/restoring it we > should > use the same value across all VCPUs. > > Reported-by: Philippe Coquard <philippe.coquard@xxxxxxxx> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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