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    Subject[PATCH 4.19 112/293] KVM: x86: Update vCPUs hv_clock before back to guest when tsc_offset is adjusted
    Date
    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
    @@ -2511,6 +2511,10 @@ 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;
    }

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