[PATCH 5.10 226/236] KVM: x86: Update vCPUs hv_clock before back to guest when tsc_offset is adjusted

Greg Kroah-Hartman
2021-09-13T13:50:36Z

From: Zelin Deng <zelin.deng@linux.alibaba.com>

commit d9130a2dfdd4b21736c91b818f87dbc0ccd1e757 upstream.

When MSR_IA32_TSC_ADJUST is written by guest due to TSC ADJUST feature
especially there's a big tsc warp (like a new vCPU is hot-added into VM
which has been up for a long time), tsc_offset is added by a large value
then go back to guest. This causes system time jump as tsc_timestamp is
not adjusted in the meantime and pvclock monotonic character.
To fix this, just notify kvm to update vCPU's guest time before back to
guest.

Cc: stable@vger.kernel.org
Signed-off-by: Zelin Deng <zelin.deng@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1619576521-81399-2-git-send-email-zelin.deng@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/x86.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3116,6 +3116,10 @@ int kvm_set_msr_common(struct kvm_vcpu *
if (!msr_info->host_initiated) {
s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
adjust_tsc_offset_guest(vcpu, adj);
+ /* Before back to guest, tsc_timestamp must be adjusted
+ * as well, otherwise guest's percpu pvclock time could jump.
+ */
+ kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
}
vcpu->arch.ia32_tsc_adjust_msr = data;
}