`next` is an `uint64_t` value, but `timer_mod` takes an `int64_t`. This
resulted in high values such as `UINT64_MAX` being converted to `-1`,
which caused an immediate timer interrupt.

By limiting `next` to `INT64_MAX` no overflow will happen while the
timer will still be effectively set to "infinitely" far in the future.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/493
Signed-off-by: David Hoppenbrouwers <david@salt-inc.org>
---
I wrongly used `MAX` instead of `MIN`. I've amended the patch.

 hw/intc/sifive_clint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/intc/sifive_clint.c b/hw/intc/sifive_clint.c
index 0f41e5ea1c..de47571fca 100644
--- a/hw/intc/sifive_clint.c
+++ b/hw/intc/sifive_clint.c
@@ -61,6 +61,8 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, uint64_t value,
     /* back to ns (note args switched in muldiv64) */
     next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
         muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq);
+    /* ensure next does not overflow, as timer_mod takes a signed value */
+    next = MIN(next, INT64_MAX);
     timer_mod(cpu->env.timer, next);
 }
 
-- 
2.20.1

On Tue, Aug 17, 2021 at 2:38 AM David Hoppenbrouwers <david@salt-inc.org> wrote:
>
> `next` is an `uint64_t` value, but `timer_mod` takes an `int64_t`. This
> resulted in high values such as `UINT64_MAX` being converted to `-1`,
> which caused an immediate timer interrupt.
>
> By limiting `next` to `INT64_MAX` no overflow will happen while the
> timer will still be effectively set to "infinitely" far in the future.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/493
> Signed-off-by: David Hoppenbrouwers <david@salt-inc.org>
> ---
> I wrongly used `MAX` instead of `MIN`. I've amended the patch.
>
>  hw/intc/sifive_clint.c | 2 ++
>  1 file changed, 2 insertions(+)
>

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

On Tue, Aug 17, 2021 at 6:00 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> On Tue, Aug 17, 2021 at 2:38 AM David Hoppenbrouwers <david@salt-inc.org> wrote:
> >
> > `next` is an `uint64_t` value, but `timer_mod` takes an `int64_t`. This
> > resulted in high values such as `UINT64_MAX` being converted to `-1`,
> > which caused an immediate timer interrupt.
> >
> > By limiting `next` to `INT64_MAX` no overflow will happen while the
> > timer will still be effectively set to "infinitely" far in the future.
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/493
> > Signed-off-by: David Hoppenbrouwers <david@salt-inc.org>
> > ---
> > I wrongly used `MAX` instead of `MIN`. I've amended the patch.
> >
> >  hw/intc/sifive_clint.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
>
> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

Thanks!

Applied to riscv-to-apply.next

Alistair

>

On Tue, Aug 17, 2021 at 4:39 AM David Hoppenbrouwers <david@salt-inc.org> wrote:
>
> `next` is an `uint64_t` value, but `timer_mod` takes an `int64_t`. This
> resulted in high values such as `UINT64_MAX` being converted to `-1`,
> which caused an immediate timer interrupt.
>
> By limiting `next` to `INT64_MAX` no overflow will happen while the
> timer will still be effectively set to "infinitely" far in the future.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/493
> Signed-off-by: David Hoppenbrouwers <david@salt-inc.org>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
> I wrongly used `MAX` instead of `MIN`. I've amended the patch.
>
>  hw/intc/sifive_clint.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/hw/intc/sifive_clint.c b/hw/intc/sifive_clint.c
> index 0f41e5ea1c..de47571fca 100644
> --- a/hw/intc/sifive_clint.c
> +++ b/hw/intc/sifive_clint.c
> @@ -61,6 +61,8 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, uint64_t value,
>      /* back to ns (note args switched in muldiv64) */
>      next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
>          muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq);
> +    /* ensure next does not overflow, as timer_mod takes a signed value */
> +    next = MIN(next, INT64_MAX);
>      timer_mod(cpu->env.timer, next);
>  }
>
> --
> 2.20.1
>
>