2017-11-13 8:55 GMT+08:00 Liran Alon <LIRAN.ALON@xxxxxxxxxx>: > > > On 13/11/17 02:52, Wanpeng Li wrote: >> >> 2017-11-13 8:44 GMT+08:00 Liran Alon <LIRAN.ALON@xxxxxxxxxx>: >>> >>> >>> >>> On 13/11/17 02:40, Wanpeng Li wrote: >>>> >>>> >>>> 2017-11-05 22:11 GMT+08:00 Liran Alon <liran.alon@xxxxxxxxxx>: >>>>> >>>>> >>>>> When guest passes KVM it's pvclock-page GPA via WRMSR to >>>>> MSR_KVM_SYSTEM_TIME / MSR_KVM_SYSTEM_TIME_NEW, KVM don't initialize >>>>> pvclock-page to some start-values. It just requests a clock-update >>>>> which >>>> >>>> >>>> >>>> KVM does, please refer to memset(hv_clock, 0, size) in kvmclock_init(). >>> >>> >>> >>> kvmclock_init() is the code that runs in KVM-guest. I was talking here >>> about >>> the code that handles the WRMSR in KVM hypervisor code. >>> >>> The issue happens when the guest doesn't init pvclock-page as done in >>> kvmclock_init(). Not all guests behave nicely :) >> >> >> But the codes which you modify just works for kvm guest I think. > > No, it's the code that runs in KVM hypervisor for any guest that knows how > to work with KVM pv-clock PV interface. > Linux guest is just one of the possible guests which can use this interface. > kvmclock_init() you mentioned is part of the linux-guest. But there are > other guests which use KVM pv-clock PV interface. Good to know it, could you point one? > > -Liran > >> >> Regards, >> Wanpeng Li >> >>> >>> -Liran >>> >>>> >>>> Regards, >>>> Wanpeng Li >>>> >>>>> will happen before entering to guest. >>>>> >>>>> The clock-update logic will call kvm_setup_pvclock_page() to update the >>>>> pvclock-page with info. However, kvm_setup_pvclock_page() *wrongly* >>>>> assumes that the version-field is initialized to an even number. This >>>>> is >>>>> wrong because at first-time write, field could be any-value. >>>>> >>>>> Fix simply makes sure that if first-time version-field is odd, >>>>> increment >>>>> it once more to make it even and only then start standard logic. >>>>> This follows same logic as done in other pvclock shared-pages (See >>>>> kvm_write_wall_clock() and record_steal_time()). >>>>> >>>>> Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx> >>>>> Reviewed-by: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx> >>>>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> >>>>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> >>>>> --- >>>>> arch/x86/kvm/x86.c | 3 +++ >>>>> 1 file changed, 3 insertions(+) >>>>> >>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>>> index 03869eb7fcd6..181106080e41 100644 >>>>> --- a/arch/x86/kvm/x86.c >>>>> +++ b/arch/x86/kvm/x86.c >>>>> @@ -1830,6 +1830,9 @@ static void kvm_setup_pvclock_page(struct >>>>> kvm_vcpu >>>>> *v) >>>>> */ >>>>> BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) >>>>> != >>>>> 0); >>>>> >>>>> + if (guest_hv_clock.version & 1) >>>>> + ++guest_hv_clock.version; /* first time write, random >>>>> junk */ >>>>> + >>>>> vcpu->hv_clock.version = guest_hv_clock.version + 1; >>>>> kvm_write_guest_cached(v->kvm, &vcpu->pv_time, >>>>> &vcpu->hv_clock, >>>>> -- >>>>> 1.9.1 >>>>> >>> >
