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. 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 >>> >
