On 21/09/20 18:23, Sean Christopherson wrote: > Avoid "should" in code comments and describe what the code is doing, not what > it should be doing. The only exception for this is when the code has a known > flaw/gap, e.g. "KVM should do X, but because of Y, KVM actually does Z". > >> + * return it's real L1 value so that its restore will be correct. > s/it's/its > > Perhaps add "unconditionally" somewhere, since arch.tsc_offset can also contain > the L1 value. E.g. > > * Unconditionally return L1's TSC offset on userspace reads > * so that userspace reads and writes always operate on L1's > * offset, e.g. to ensure deterministic behavior for migration. > */ > Technically the host need not restore MSR_IA32_TSC at all. This follows the idea of the discussion with Oliver Upton about transmitting the state of the kvmclock heuristics to userspace, which include a (TSC, CLOCK_MONOTONIC) pair to transmit the offset to the destination. All that needs to be an L1 value is then the TSC value in that pair. I'm a bit torn over this patch. On one hand it's an easy solution, on the other hand it's... just wrong if KVM_GET_MSR is used for e.g. debugging the guest. I'll talk to Maxim and see if he can work on the kvmclock migration stuff. Paolo
