On Fri, Sep 20, 2019 at 10:33 PM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: > > Suleiman Souhlal <suleiman@xxxxxxxxxx> writes: > > > When CONFIG_KVMCLOCK_HOST_TIMEKEEPING is enabled, and the host > > supports it, update our timekeeping parameters to be the same as > > the host. This lets us have our time synchronized with the host's, > > even in the presence of host NTP or suspend. > > > > When enabled, kvmclock uses raw tsc instead of pvclock. > > > > When enabled, syscalls that can change time, such as settimeofday(2) > > or adj_timex(2) are disabled in the guest. > > > > Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx> > > --- > > arch/x86/Kconfig | 9 +++ > > arch/x86/include/asm/kvmclock.h | 2 + > > arch/x86/kernel/kvmclock.c | 127 +++++++++++++++++++++++++++++++- > > kernel/time/timekeeping.c | 21 ++++++ > > 4 files changed, 155 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 4195f44c6a09..37299377d9d7 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -837,6 +837,15 @@ config PARAVIRT_TIME_ACCOUNTING > > config PARAVIRT_CLOCK > > bool > > > > +config KVMCLOCK_HOST_TIMEKEEPING > > + bool "kvmclock uses host timekeeping" > > + depends on KVM_GUEST > > + ---help--- > > + Select this option to make the guest use the same timekeeping > > + parameters as the host. This means that time will be almost > > + exactly the same between the two. Only works if the host uses "tsc" > > + clocksource. > > + > > I'd also like to speak up against this config, it is confusing. In case > the goal is to come up with a TSC-based clock for guests which will > return the same as clock_gettime() on the host (or, is the goal to just > have the same reading for all guests on the host?) I'd suggest we create > a separate (from KVMCLOCK) clocksource (mirroring host timekeeper) and > guests will be free to pick the one they like. Fair enough. I'll do that in the next version of the patch. The goal is to have a guest clock that gives the same clock_gettime(CLOCK_MONOTONIC) as the host. Thanks, -- Suleiman
