From e880c6ea55b9805294ecc100ee95e0c9860ae90e Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Tue, 16 Mar 2021 15:37:34 +0100 Subject: [PATCH] KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs When KVM_REQ_MASTERCLOCK_UPDATE request is issued (e.g. after migration) we need to make sure no vCPU sees stale values in PV clock structures and thus all vCPUs are kicked with KVM_REQ_CLOCK_UPDATE. Hyper-V TSC page clocksource is global and kvm_guest_time_update() only updates in on vCPU0 but this is not entirely correct: nothing blocks some other vCPU from entering the guest before we finish the update on CPU0 and it can read stale values from the page. Invalidate TSC page in kvm_gen_update_masterclock() to switch all vCPUs to using MSR based clocksource (HV_X64_MSR_TIME_REF_COUNT). Signed-off-by: Vitaly Kuznetsov Message-Id: <20210316143736.964151-3-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/hyperv.c | 23 +++++++++++++++++++++++ arch/x86/kvm/hyperv.h | 1 + arch/x86/kvm/x86.c | 2 ++ 3 files changed, 26 insertions(+) diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index eefb85b86fe84a..a0e3c49233d4cc 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -1137,6 +1137,29 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, mutex_unlock(&hv->hv_lock); } +void kvm_hv_invalidate_tsc_page(struct kvm *kvm) +{ + struct kvm_hv *hv = to_kvm_hv(kvm); + u64 gfn; + + if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)) + return; + + mutex_lock(&hv->hv_lock); + + if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)) + goto out_unlock; + + gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT; + + hv->tsc_ref.tsc_sequence = 0; + kvm_write_guest(kvm, gfn_to_gpa(gfn), + &hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence)); + +out_unlock: + mutex_unlock(&hv->hv_lock); +} + static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host) { diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h index e951af1fcb2c59..60547d5cb6d724 100644 --- a/arch/x86/kvm/hyperv.h +++ b/arch/x86/kvm/hyperv.h @@ -133,6 +133,7 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu); void kvm_hv_setup_tsc_page(struct kvm *kvm, struct pvclock_vcpu_time_info *hv_clock); +void kvm_hv_invalidate_tsc_page(struct kvm *kvm); void kvm_hv_init_vm(struct kvm *kvm); void kvm_hv_destroy_vm(struct kvm *kvm); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 47e021bdcc94ab..a5c5b38735e196 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2551,6 +2551,8 @@ static void kvm_gen_update_masterclock(struct kvm *kvm) struct kvm_vcpu *vcpu; struct kvm_arch *ka = &kvm->arch; + kvm_hv_invalidate_tsc_page(kvm); + spin_lock(&ka->pvclock_gtod_sync_lock); kvm_make_mclock_inprogress_request(kvm); /* no guest entries from this point */