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

[Pavel Dovgalyuk]

On 27.10.2021 07:05, Jason Wang wrote:
> 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?

Not really. I think there could be several solutions:
1. Save some flag to distinguish between old and new state.
2. Use deterministic version for icount (or even record/replay) mode only.
3. Check machine type to change the behavior (as Dave proposed)

> 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
> >       }
> >   };