Commit 00f4d64e authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Paolo Bonzini
Browse files

kvmclock: clock should count only if vm is running 



kvmclock should not count while vm is paused, because:

1) if the vm is paused for long periods, timekeeping
math can overflow while converting the (large) clocksource
delta to nanoseconds.

2) Users rely on CLOCK_MONOTONIC to count run time, that is,
time which OS has been in a runnable state (see CLOCK_BOOTTIME).

Change kvmclock driver so as to save clock value when vm transitions
from runnable to stopped state, and to restore clock value from stopped
to runnable transition.

Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarGleb Natapov <gleb@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent bd50cbaa

hw/i386/kvm/clock.c

+30 −34
Original line number Diff line number Diff line
@@ -28,38 +28,6 @@ typedef struct KVMClockState { 
    bool clock_valid;

} KVMClockState;



static void kvmclock_pre_save(void *opaque)

{

    KVMClockState *s = opaque;

    struct kvm_clock_data data;

    int ret;



    if (s->clock_valid) {

        return;

    }

    ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);

    if (ret < 0) {

        fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));

        data.clock = 0;

    }

    s->clock = data.clock;

    /*

     * If the VM is stopped, declare the clock state valid to avoid re-reading

     * it on next vmsave (which would return a different value). Will be reset

     * when the VM is continued.

     */

    s->clock_valid = !runstate_is_running();

}



static int kvmclock_post_load(void *opaque, int version_id)

{

    KVMClockState *s = opaque;

    struct kvm_clock_data data;



    data.clock = s->clock;

    data.flags = 0;

    return kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);

}



static void kvmclock_vm_state_change(void *opaque, int running,

                                     RunState state)
@@ -70,8 +38,18 @@ static void kvmclock_vm_state_change(void *opaque, int running, 
    int ret;



    if (running) {

        struct kvm_clock_data data;



        s->clock_valid = false;



        data.clock = s->clock;

        data.flags = 0;

        ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);

        if (ret < 0) {

            fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));

            abort();

        }



        if (!cap_clock_ctrl) {

            return;

        }
@@ -84,6 +62,26 @@ static void kvmclock_vm_state_change(void *opaque, int running, 
                return;

            }

        }

    } else {

        struct kvm_clock_data data;

        int ret;



        if (s->clock_valid) {

            return;

        }

        ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);

        if (ret < 0) {

            fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));

            abort();

        }

        s->clock = data.clock;



        /*

         * If the VM is stopped, declare the clock state valid to

         * avoid re-reading it on next vmsave (which would return

         * a different value). Will be reset when the VM is continued.

         */

        s->clock_valid = true;

    }

}
@@ -100,8 +98,6 @@ static const VMStateDescription kvmclock_vmsd = { 
    .version_id = 1,

    .minimum_version_id = 1,

    .minimum_version_id_old = 1,

    .pre_save = kvmclock_pre_save,

    .post_load = kvmclock_post_load,

    .fields = (VMStateField[]) {

        VMSTATE_UINT64(clock, KVMClockState),

        VMSTATE_END_OF_LIST()