[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 2/2] x86/HVM: Use fixed TSC value when saving or restoring domain
On 04/01/2014 11:53 AM, Boris Ostrovsky 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. (As part of the patch, update rdtscll's definition so that its variables don't clash with outer code) Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> This patch will need to be updated as it doesn't quite fix the problem on some AMD processors (they may do one extra rdtsc in svm_set_tsc_offset()). -boris _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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