RE: [PATCH v3] xen/arm: avoid overflow when setting vtimer in context switch

[Jiamei Xie <Jiamei.Xie@xxxxxxx>]

Hi,

> -----Original Message-----
> From: Jiamei Xie <jiamei.xie@xxxxxxx>
> Sent: 2022年6月30日 9:54
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Jiamei Xie <Jiamei.Xie@xxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Bertrand Marquis
> <Bertrand.Marquis@xxxxxxx>; Volodymyr Babchuk
> <Volodymyr_Babchuk@xxxxxxxx>; Wei Chen <Wei.Chen@xxxxxxx>
> Subject: [PATCH v3] xen/arm: avoid overflow when setting vtimer in context
> switch
> 
> virt_vtimer_save is calculating the new time for the vtimer in:
> "v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
> - boot_count".
> In this formula, "cval + offset" might cause uint64_t overflow.
> Changing it to "ticks_to_ns(v->domain->arch.virt_timer_base.offset -
> boot_count) + ticks_to_ns(v->arch.virt_timer.cval)" can avoid overflow,
> and "ticks_to_ns(arch.virt_timer_base.offset - boot_count)" will be
> always the same, which has been caculated in domain_vtimer_init.
> Introduce a new field virt_timer_base.nanoseconds to store this value
> for arm in struct arch_domain, so we can use it directly.
> 
> Signed-off-by: Jiamei Xie <jiamei.xie@xxxxxxx>
> Change-Id: Ib80cee51eaf844661e6f92154a0339ad2a652f9b

I am sorry I forget to remove the Change-Id.

> ---
> was "xen/arm: avoid vtimer flip-flop transition in context switch".
> v3 changes:
> -re-write commit message
> -store nanoseconds in virt_timer_base instead of adding a new structure
> -assign to nanoseconds first, then seconds
> ---
>  xen/arch/arm/include/asm/domain.h | 1 +
>  xen/arch/arm/vtimer.c             | 9 ++++++---
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/domain.h
> b/xen/arch/arm/include/asm/domain.h
> index ed63c2b6f9..cd9ce19b4b 100644
> --- a/xen/arch/arm/include/asm/domain.h
> +++ b/xen/arch/arm/include/asm/domain.h
> @@ -71,6 +71,7 @@ struct arch_domain
> 
>      struct {
>          uint64_t offset;
> +        s_time_t nanoseconds;
>      } virt_timer_base;
> 
>      struct vgic_dist vgic;
> diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
> index 6b78fea77d..aeaea78e4c 100644
> --- a/xen/arch/arm/vtimer.c
> +++ b/xen/arch/arm/vtimer.c
> @@ -63,7 +63,9 @@ static void virt_timer_expired(void *data)
>  int domain_vtimer_init(struct domain *d, struct xen_arch_domainconfig
> *config)
>  {
>      d->arch.virt_timer_base.offset = get_cycles();
> -    d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset -
> boot_count);
> +    d->arch.virt_timer_base.nanoseconds =
> +        ticks_to_ns(d->arch.virt_timer_base.offset - boot_count);
> +    d->time_offset.seconds = d->arch.virt_timer_base.nanoseconds;
>      do_div(d->time_offset.seconds, 1000000000);
> 
>      config->clock_frequency = timer_dt_clock_frequency;
> @@ -144,8 +146,9 @@ void virt_timer_save(struct vcpu *v)
>      if ( (v->arch.virt_timer.ctl & CNTx_CTL_ENABLE) &&
>           !(v->arch.virt_timer.ctl & CNTx_CTL_MASK))
>      {
> -        set_timer(&v->arch.virt_timer.timer, 
> ticks_to_ns(v->arch.virt_timer.cval
> +
> -                  v->domain->arch.virt_timer_base.offset - boot_count));
> +        set_timer(&v->arch.virt_timer.timer,
> +                  v->domain->arch.virt_timer_base.nanoseconds +
> +                  ticks_to_ns(v->arch.virt_timer.cval));
>      }
>  }
> 
> --
> 2.25.1