On 13/11/2017 07:47, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> There is a logic to handle first-time write when updating the
> pvclock/wall clock/steal time shared memory pages each time,
> actually we should do this logic during pv stuffs setup if we
> suspect the version-field can't be guranteed to be initialized
> to an even number by the guest. This patch fixes it by handling
> the first-time write of pvclock/steal time during setup since
> the update is frequent, and keeping the wall clock since it is
> rare updating.
The cost is almost zero, and the code is smaller without this patch, so
I think it's a little better to leave things as is.
Paolo
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 29 ++++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4552427..19311e0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1833,9 +1833,6 @@ 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,
> @@ -2126,9 +2123,6 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>
> vcpu->arch.st.steal.preempted = 0;
>
> - if (vcpu->arch.st.steal.version & 1)
> - vcpu->arch.st.steal.version += 1; /* first time write, random junk */
> -
> vcpu->arch.st.steal.version += 1;
>
> kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
> @@ -2256,8 +2250,19 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> &vcpu->arch.pv_time, data & ~1ULL,
> sizeof(struct pvclock_vcpu_time_info)))
> vcpu->arch.pv_time_enabled = false;
> - else
> + else {
> + struct pvclock_vcpu_time_info guest_hv_clock;
> +
> vcpu->arch.pv_time_enabled = true;
> + if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.pv_time,
> + &guest_hv_clock, sizeof(guest_hv_clock))))
> + break;
> + if (guest_hv_clock.version & 1)
> + ++guest_hv_clock.version; /* first time write, random junk */
> + kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.pv_time,
> + &vcpu->arch.hv_clock,
> + sizeof(vcpu->arch.hv_clock.version));
> + }
>
> break;
> }
> @@ -2283,6 +2288,16 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> if (!(data & KVM_MSR_ENABLED))
> break;
>
> + if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
> + &vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
> + break;
> +
> + if (vcpu->arch.st.steal.version & 1)
> + vcpu->arch.st.steal.version += 1; /* first time write, random junk */
> +
> + kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
> + &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
> +
> kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
>
> break;
>
