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KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs

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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 <vkuznets@redhat.com>
Message-Id: <20210316143736.964151-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2021-03-16 15:37:34 +01:00 committed by Paolo Bonzini
parent d2547cf597
commit e880c6ea55
3 changed files with 26 additions and 0 deletions
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23
arch/x86/kvm/hyperv.c
View file

@ -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)
{

1
arch/x86/kvm/hyperv.h
View file

@ -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);

2
arch/x86/kvm/x86.c
View file

@ -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 */