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    SubjectRe: [PATCH] kvm: notify host when guest paniced
    On 2012-02-28 09:23, Wen Congyang wrote:
    > At 02/27/2012 11:08 PM, Jan Kiszka Wrote:
    >> On 2012-02-27 04:01, Wen Congyang wrote:
    >>> We can know the guest is paniced when the guest runs on xen.
    >>> But we do not have such feature on kvm. This patch implemnts
    >>> this feature, and the implementation is the same as xen:
    >>> register panic notifier, and call hypercall when the guest
    >>> is paniced.
    >>>
    >>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
    >>> ---
    >>> arch/x86/kernel/kvm.c | 12 ++++++++++++
    >>> arch/x86/kvm/svm.c | 8 ++++++--
    >>> arch/x86/kvm/vmx.c | 8 ++++++--
    >>> arch/x86/kvm/x86.c | 13 +++++++++++--
    >>> include/linux/kvm.h | 1 +
    >>> include/linux/kvm_para.h | 1 +
    >>> 6 files changed, 37 insertions(+), 6 deletions(-)
    >>>
    >>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
    >>> index f0c6fd6..b928d1d 100644
    >>> --- a/arch/x86/kernel/kvm.c
    >>> +++ b/arch/x86/kernel/kvm.c
    >>> @@ -331,6 +331,17 @@ static struct notifier_block kvm_pv_reboot_nb = {
    >>> .notifier_call = kvm_pv_reboot_notify,
    >>> };
    >>>
    >>> +static int
    >>> +kvm_pv_panic_notify(struct notifier_block *nb, unsigned long code, void *unused)
    >>> +{
    >>> + kvm_hypercall0(KVM_HC_GUEST_PANIC);
    >>> + return NOTIFY_DONE;
    >>> +}
    >>> +
    >>> +static struct notifier_block kvm_pv_panic_nb = {
    >>> + .notifier_call = kvm_pv_panic_notify,
    >>> +};
    >>> +
    >>
    >> You should split up host and guest-side changes.
    >>
    >>> static u64 kvm_steal_clock(int cpu)
    >>> {
    >>> u64 steal;
    >>> @@ -417,6 +428,7 @@ void __init kvm_guest_init(void)
    >>>
    >>> paravirt_ops_setup();
    >>> register_reboot_notifier(&kvm_pv_reboot_nb);
    >>> + atomic_notifier_chain_register(&panic_notifier_list, &kvm_pv_panic_nb);
    >>> for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
    >>> spin_lock_init(&async_pf_sleepers[i].lock);
    >>> if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
    >>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
    >>> index 0b7690e..38b4705 100644
    >>> --- a/arch/x86/kvm/svm.c
    >>> +++ b/arch/x86/kvm/svm.c
    >>> @@ -1900,10 +1900,14 @@ static int halt_interception(struct vcpu_svm *svm)
    >>>
    >>> static int vmmcall_interception(struct vcpu_svm *svm)
    >>> {
    >>> + int ret;
    >>> +
    >>> svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
    >>> skip_emulated_instruction(&svm->vcpu);
    >>> - kvm_emulate_hypercall(&svm->vcpu);
    >>> - return 1;
    >>> + ret = kvm_emulate_hypercall(&svm->vcpu);
    >>> +
    >>> + /* Ignore the error? */
    >>> + return ret == 0 ? 0 : 1;
    >>
    >> Why can't kvm_emulate_hypercall return the right value?
    >
    > kvm_emulate_hypercall() will call kvm_hv_hypercall(), and
    > kvm_hv_hypercall() will return 0 when vcpu's CPL > 0.
    > If vcpu's CPL > 0, does kvm need to exit and tell it to
    > qemu?

    No, there is currently no exit to userspace due to hypercalls, neither
    of HV nor KVM kind.

    The point is that the return code of kvm_emulate_hypercall is unused so
    far, so you can easily redefine it to encode continue vs. exit to
    userspace. Once someone has different needs, this could still be
    refactored again.

    Jan

    --
    Siemens AG, Corporate Technology, CT T DE IT 1
    Corporate Competence Center Embedded Linux


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