Re: [PATCH] hw/net: store timers for e1000 in vmstate

[Jason Wang <jasowang@redhat.com>]

On Tue, Oct 26, 2021 at 6:36 PM Pavel Dovgalyuk
<pavel.dovgalyuk@ispras.ru> wrote:
>
> Setting timers randomly when vmstate is loaded breaks
> execution determinism.
> Therefore this patch allows saving mit and autoneg timers
> for e1000. It makes execution deterministic and allows
> snapshotting and reverse debugging in icount mode.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> ---
>  hw/net/e1000.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 50 insertions(+), 11 deletions(-)
>
> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index a30546c5d5..2f706f7298 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -37,6 +37,7 @@
>  #include "qemu/iov.h"
>  #include "qemu/module.h"
>  #include "qemu/range.h"
> +#include "sysemu/replay.h"
>
>  #include "e1000x_common.h"
>  #include "trace.h"
> @@ -1407,7 +1408,7 @@ static int e1000_pre_save(void *opaque)
>       * complete auto-negotiation immediately. This allows us to look
>       * at MII_SR_AUTONEG_COMPLETE to infer link status on load.
>       */
> -    if (nc->link_down && have_autoneg(s)) {
> +    if (replay_mode == REPLAY_MODE_NONE && nc->link_down && have_autoneg(s)) {
>          s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
>      }
>
> @@ -1438,22 +1439,12 @@ static int e1000_post_load(void *opaque, int version_id)
>              s->mac_reg[TADV] = 0;
>          s->mit_irq_level = false;
>      }
> -    s->mit_ide = 0;
> -    s->mit_timer_on = true;
> -    timer_mod(s->mit_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 1);
>
>      /* nc.link_down can't be migrated, so infer link_down according
>       * to link status bit in mac_reg[STATUS].
>       * Alternatively, restart link negotiation if it was in progress. */
>      nc->link_down = (s->mac_reg[STATUS] & E1000_STATUS_LU) == 0;
>
> -    if (have_autoneg(s) &&
> -        !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE)) {
> -        nc->link_down = false;
> -        timer_mod(s->autoneg_timer,
> -                  qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 500);
> -    }

So we won't get those timers armed after migration unconditionally. Is
this intended?

Thanks

> -
>      s->tx.props = s->mig_props;
>      if (!s->received_tx_tso) {
>          /* We received only one set of offload data (tx.props)
> @@ -1472,6 +1463,13 @@ static int e1000_tx_tso_post_load(void *opaque, int version_id)
>      return 0;
>  }
>
> +static int e1000_mit_timer_post_load(void *opaque, int version_id)
> +{
> +    E1000State *s = opaque;
> +    s->mit_timer_on = true;
> +    return 0;
> +}
> +
>  static bool e1000_mit_state_needed(void *opaque)
>  {
>      E1000State *s = opaque;
> @@ -1493,6 +1491,21 @@ static bool e1000_tso_state_needed(void *opaque)
>      return chkflag(TSO);
>  }
>
> +static bool e1000_mit_timer_needed(void *opaque)
> +{
> +    E1000State *s = opaque;
> +
> +    return s->mit_timer_on;
> +}
> +
> +static bool e1000_autoneg_timer_needed(void *opaque)
> +{
> +    E1000State *s = opaque;
> +
> +    return have_autoneg(s)
> +           && !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE);
> +}
> +
>  static const VMStateDescription vmstate_e1000_mit_state = {
>      .name = "e1000/mit_state",
>      .version_id = 1,
> @@ -1541,6 +1554,30 @@ static const VMStateDescription vmstate_e1000_tx_tso_state = {
>      }
>  };
>
> +static const VMStateDescription vmstate_e1000_mit_timer = {
> +    .name = "e1000/mit_timer",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = e1000_mit_timer_needed,
> +    .post_load = e1000_mit_timer_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_TIMER_PTR(mit_timer, E1000State),
> +        VMSTATE_UINT32(mit_ide, E1000State),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static const VMStateDescription vmstate_e1000_autoneg_timer = {
> +    .name = "e1000/autoneg_timer",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = e1000_autoneg_timer_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_TIMER_PTR(autoneg_timer, E1000State),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static const VMStateDescription vmstate_e1000 = {
>      .name = "e1000",
>      .version_id = 2,
> @@ -1622,6 +1659,8 @@ static const VMStateDescription vmstate_e1000 = {
>          &vmstate_e1000_mit_state,
>          &vmstate_e1000_full_mac_state,
>          &vmstate_e1000_tx_tso_state,
> +        &vmstate_e1000_mit_timer,
> +        &vmstate_e1000_autoneg_timer,
>          NULL
>      }
>  };
>