Commit 0cdd3d14 authored by Jan Kiszka's avatar Jan Kiszka Committed by Avi Kivity
Browse files

kvm: i8254: Fix conversion of in-kernel to userspace state 



Due to a offset between the clock used to generate the in-kernel
count_load_time (CLOCK_MONOTONIC) and the clock used for processing this
in userspace (vm_clock), reading back the output of PIT channel 2 via
port 0x61 was broken. One use cases that suffered from it was the CPU
frequency calibration of SeaBIOS, which also affected IDE/AHCI timeouts.

This fixes it by calibrating the offset between both clocks on
kvm_pit_get and adjusting the kernel value before saving it in the
userspace state. As the calibration only works while the vm_clock is
running, we cache the in-kernel state across stopped phases.

Signed-off-by: default avatarJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 0614cb82

hw/kvm/i8254.c

+52 −5
Original line number Diff line number Diff line
@@ -23,31 +23,63 @@ 
 * THE SOFTWARE.

 */

#include "qemu-timer.h"

#include "sysemu.h"

#include "hw/i8254.h"

#include "hw/i8254_internal.h"

#include "kvm.h"



#define KVM_PIT_REINJECT_BIT 0



#define CALIBRATION_ROUNDS   3



typedef struct KVMPITState {

    PITCommonState pit;

    LostTickPolicy lost_tick_policy;

    bool state_valid;

} KVMPITState;



static void kvm_pit_get(PITCommonState *s)

static int64_t abs64(int64_t v)

{

    return v < 0 ? -v : v;

}



static void kvm_pit_get(PITCommonState *pit)

{

    KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);

    struct kvm_pit_state2 kpit;

    struct kvm_pit_channel_state *kchan;

    struct PITChannelState *sc;

    int64_t offset, clock_offset;

    struct timespec ts;

    int i, ret;



    if (s->state_valid) {

        return;

    }



    /*

     * Measure the delta between CLOCK_MONOTONIC, the base used for

     * kvm_pit_channel_state::count_load_time, and vm_clock. Take the

     * minimum of several samples to filter out scheduling noise.

     */

    clock_offset = INT64_MAX;

    for (i = 0; i < CALIBRATION_ROUNDS; i++) {

        offset = qemu_get_clock_ns(vm_clock);

        clock_gettime(CLOCK_MONOTONIC, &ts);

        offset -= ts.tv_nsec;

        offset -= (int64_t)ts.tv_sec * 1000000000;

        if (abs64(offset) < abs64(clock_offset)) {

            clock_offset = offset;

        }

    }



    if (kvm_has_pit_state2()) {

        ret = kvm_vm_ioctl(kvm_state, KVM_GET_PIT2, &kpit);

        if (ret < 0) {

            fprintf(stderr, "KVM_GET_PIT2 failed: %s\n", strerror(ret));

            abort();

        }

        s->channels[0].irq_disabled = kpit.flags & KVM_PIT_FLAGS_HPET_LEGACY;

        pit->channels[0].irq_disabled = kpit.flags & KVM_PIT_FLAGS_HPET_LEGACY;

    } else {

        /*

         * kvm_pit_state2 is superset of kvm_pit_state struct,
@@ -61,7 +93,7 @@ static void kvm_pit_get(PITCommonState *s) 
    }

    for (i = 0; i < 3; i++) {

        kchan = &kpit.channels[i];

        sc = &s->channels[i];

        sc = &pit->channels[i];

        sc->count = kchan->count;

        sc->latched_count = kchan->latched_count;

        sc->count_latched = kchan->count_latched;
@@ -74,10 +106,10 @@ static void kvm_pit_get(PITCommonState *s) 
        sc->mode = kchan->mode;

        sc->bcd = kchan->bcd;

        sc->gate = kchan->gate;

        sc->count_load_time = kchan->count_load_time;

        sc->count_load_time = kchan->count_load_time + clock_offset;

    }



    sc = &s->channels[0];

    sc = &pit->channels[0];

    sc->next_transition_time =

        pit_get_next_transition_time(sc, sc->count_load_time);

}
@@ -173,6 +205,19 @@ static void kvm_pit_irq_control(void *opaque, int n, int enable) 
    kvm_pit_put(pit);

}



static void kvm_pit_vm_state_change(void *opaque, int running,

                                    RunState state)

{

    KVMPITState *s = opaque;



    if (running) {

        s->state_valid = false;

    } else {

        kvm_pit_get(&s->pit);

        s->state_valid = true;

    }

}



static int kvm_pit_initfn(PITCommonState *pit)

{

    KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
@@ -215,6 +260,8 @@ static int kvm_pit_initfn(PITCommonState *pit) 


    qdev_init_gpio_in(&pit->dev.qdev, kvm_pit_irq_control, 1);



    qemu_add_vm_change_state_handler(kvm_pit_vm_state_change, s);



    return 0;

}