KVM: x86: Update vCPU's hv_clock before back to guest when tsc_offset is adjusted

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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1a00af1b076b6d8dfc1dbba20a4d09350c22e9ae..28ef14155726461ec935c711ce8cc0ebe22c0bdf 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3321,6 +3321,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                        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;
                }