Re: [PATCH 2/3] hw/intc: Save timers array in RISC-V mtimer VMState

[Peter Xu <peterx@redhat.com>]

On Tue, Sep 09, 2025 at 09:45:07AM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 9/9/25 6:46 AM, TANG Tiancheng wrote:
> > The current 'timecmp' field in vmstate_riscv_mtimer is insufficient to keep
> > timers functional after migration.
> > 
> > If an mtimer's entry in 'mtimer->timers' is active at the time the snapshot
> > is taken, it means riscv_aclint_mtimer_write_timecmp() has written to
> > 'mtimecmp' and scheduled a timer into QEMU's main loop 'timer_list'.
> > 
> > During snapshot save, these active timers must also be migrated; otherwise,
> > after snapshot load there is no mechanism to restore 'mtimer->timers' back
> > into the 'timer_list', and any pending timer events would be lost.
> > 
> > QEMU's migration framework commonly uses VMSTATE_TIMER_xxx macros to save
> > and restore 'QEMUTimer' variables. However, 'timers' is a pointer array
> > with variable length, and vmstate.h did not previously provide a helper
> > macro for such type.
> > 
> > This commit adds a new macro, 'VMSTATE_TIMER_PTR_VARRAY', to handle saving
> > and restoring a variable-length array of 'QEMUTimer *'. We then use this
> > macro to migrate the 'mtimer->timers' array, ensuring that timer events
> > remain scheduled correctly after snapshot load.
> > 
> > Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
> > Signed-off-by: TANG Tiancheng <lyndra@linux.alibaba.com>
> > ---
> 
> LGTM but I wonder if changing one of the VMSTATE_TIMER_xxxx macros to accept
> variable length arrays is better than creating a new macro that only RISC-V
> cares about. Creating a new macro surely is easier and less messier than
> changing all existing callers though ...
> 
> I'll let the migration folks weight in. Thanks,

I didn't see a 2nd user, though..

I'd split VMSTATE_VARRAY_OF_POINTER_UINT32() into a separate patch, then
define VMSTATE_TIMER_PTR_VARRAY() in riscv .c files if that's the only
user, and if that helps readability.

Thanks,

> 
> Daniel
> 
> 
> 
> >   hw/intc/riscv_aclint.c      |  6 ++++--
> >   include/migration/vmstate.h | 14 ++++++++++++++
> >   2 files changed, 18 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/intc/riscv_aclint.c b/hw/intc/riscv_aclint.c
> > index 318a9c8248432a8cd4c3f3fa990739917ecf7ca1..9f4c36e965e2aa379d75c0a9f656177f0dd82a45 100644
> > --- a/hw/intc/riscv_aclint.c
> > +++ b/hw/intc/riscv_aclint.c
> > @@ -323,13 +323,15 @@ static void riscv_aclint_mtimer_reset_enter(Object *obj, ResetType type)
> >   static const VMStateDescription vmstate_riscv_mtimer = {
> >       .name = "riscv_mtimer",
> > -    .version_id = 2,
> > -    .minimum_version_id = 2,
> > +    .version_id = 3,
> > +    .minimum_version_id = 3,
> >       .fields = (const VMStateField[]) {
> >               VMSTATE_UINT64(time_delta, RISCVAclintMTimerState),
> >               VMSTATE_VARRAY_UINT32(timecmp, RISCVAclintMTimerState,
> >                                     num_harts, 0,
> >                                     vmstate_info_uint64, uint64_t),
> > +            VMSTATE_TIMER_PTR_VARRAY(timers, RISCVAclintMTimerState,
> > +                                     num_harts),
> >               VMSTATE_END_OF_LIST()
> >           }
> >   };
> > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> > index 1ff7bd9ac425ba67cd5ca7ad97bcf570f9e19abe..255e403e5a103188712425d95a719d181e1a7202 100644
> > --- a/include/migration/vmstate.h
> > +++ b/include/migration/vmstate.h
> > @@ -522,6 +522,16 @@ extern const VMStateInfo vmstate_info_qlist;
> >       .offset     = vmstate_offset_array(_s, _f, _type*, _n),          \
> >   }
> > +#define VMSTATE_VARRAY_OF_POINTER_UINT32(_field, _state, _field_num, _version, _info, _type) { \
> > +    .name       = (stringify(_field)),                                    \
> > +    .version_id = (_version),                                             \
> > +    .num_offset = vmstate_offset_value(_state, _field_num, uint32_t),     \
> > +    .info       = &(_info),                                               \
> > +    .size       = sizeof(_type),                                          \
> > +    .flags      = VMS_VARRAY_UINT32 | VMS_ARRAY_OF_POINTER | VMS_POINTER, \
> > +    .offset     = vmstate_offset_pointer(_state, _field, _type),          \
> > +}
> > +
> >   #define VMSTATE_STRUCT_SUB_ARRAY(_field, _state, _start, _num, _version, _vmsd, _type) { \
> >       .name       = (stringify(_field)),                                     \
> >       .version_id = (_version),                                              \
> > @@ -1035,6 +1045,10 @@ extern const VMStateInfo vmstate_info_qlist;
> >   #define VMSTATE_TIMER_PTR_ARRAY(_f, _s, _n)                              \
> >       VMSTATE_ARRAY_OF_POINTER(_f, _s, _n, 0, vmstate_info_timer, QEMUTimer *)
> > +#define VMSTATE_TIMER_PTR_VARRAY(_f, _s, _f_n)                        \
> > +VMSTATE_VARRAY_OF_POINTER_UINT32(_f, _s, _f_n, 0, vmstate_info_timer, \
> > +                                                        QEMUTimer *)
> > +
> >   #define VMSTATE_TIMER_TEST(_f, _s, _test)                             \
> >       VMSTATE_SINGLE_TEST(_f, _s, _test, 0, vmstate_info_timer, QEMUTimer)
> > 
> 

-- 
Peter Xu