Re: [QEMU PATCH] kvmclock: advance clock by time window between vm_stop and pre_save

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/11/2016 16:25, Radim Krčmář wrote:
>> >  
>> > +        if (s->advance_clock && s->clock + s->advance_clock > s->clock) {
>> > +            s->clock += s->advance_clock;
>> > +            s->advance_clock = 0;
>> > +        }
> Can't the advance_clock added to the migrated KVMClockState instead of
> passing it as another parameter?
> 
> (It is sad that we can't just query KVMClockState in kvmclock_pre_save
>  because of the Linux bug.)

What Linux bug?  The one that makes us use kvmclock_current_nsec?

It should work with 4.9-rc (well, once Linus applies my pull request).
4.9-rc will not return ktime_get_ns for KVM_GET_CLOCK; it will return
the raw value from the kernel timekeeper.

I'm thinking that we should add a KVM capability for this, and skip
kvmclock_current_nsec if the capability is present.  The first part is
trivial, so we can do it even during Linux rc period.

Paolo