Re: [PATCH v2 10/19] target/ppc: Migrate DECR SPR

["Nicholas Piggin" <npiggin@gmail.com>]

On Wed Aug 9, 2023 at 10:56 PM AEST, Cédric Le Goater wrote:
> Hello Nick,
>
> On 8/8/23 06:19, Nicholas Piggin wrote:
> > TCG does not maintain the DEC reigster in the SPR array, so it does get
> > migrated. TCG also needs to re-start the decrementer timer on the
> > destination machine.
> > 
> > Load and store the decrementer into the SPR when migrating. This works
> > for the level-triggered (book3s) decrementer, and should be compatible
> > with existing KVM machines that do keep the DEC value there.
> > 
> > This fixes lost decrementer interrupt on migration that can cause
> > hangs, as well as other problems including record-replay bugs.
> > 
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >   target/ppc/machine.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> > 
> > diff --git a/target/ppc/machine.c b/target/ppc/machine.c
> > index 8234e35d69..8a190c4853 100644
> > --- a/target/ppc/machine.c
> > +++ b/target/ppc/machine.c
> > @@ -209,6 +209,14 @@ static int cpu_pre_save(void *opaque)
> >       /* Used to retain migration compatibility for pre 6.0 for 601 machines. */
> >       env->hflags_compat_nmsr = 0;
> >   
> > +    if (tcg_enabled()) {
> > +        /*
> > +         * TCG does not maintain the DECR spr (unlike KVM) so have to save
> > +         * it here.
> > +         */
> > +        env->spr[SPR_DECR] = cpu_ppc_load_decr(env);
> > +    }
> > +
> >       return 0;
> >   }
> >   
> > @@ -319,6 +327,12 @@ static int cpu_post_load(void *opaque, int version_id)
> >           ppc_update_ciabr(env);
> >           ppc_update_daw0(env);
> >   #endif
> > +        /*
> > +         * TCG needs to re-start the decrementer timer and/or raise the
> > +         * interrupt. This works for level-triggered decrementer. Edge
> > +         * triggered types (including HDEC) would need to carry more state.
> > +         */
> > +        cpu_ppc_store_decr(env, env->spr[SPR_DECR]);
> >           pmu_mmcr01_updated(env);
> >       }
>
>
> This doesn't apply. I am missing some patch ?

Oh, it's a small dependency on the debug patches, sorry forgot to
mention (see the ciabr/daw0 in the top of the context).

Thanks,
Nick