Re: [PATCH v4] xen/arm: avoid overflow when setting vtimer in context switch

[Julien Grall <julien@xxxxxxx>]

Hi Bertrand,

On 07/07/2022 16:35, Bertrand Marquis wrote:
> Hi Julien,
>
> > On 7 Jul 2022, at 16:33, Julien Grall <julien@xxxxxxx> wrote:
> >
> > Hi Jiamei,
> >
> > On 06/07/2022 09:25, Jiamei Xie wrote:
> > > virt_vtimer_save() will calculate the next deadline when the vCPU is
> > > scheduled out. At the moment, Xen will use the following equation:
> > > virt_timer.cval + virt_time_base.offset - boot_count
> > > The three values are 64-bit and one (cval) is controlled by domain. In
> > > theory, it would be possible that the domain has started a long time
> > > after the system boot. So virt_time_base.offset - boot_count may be a
> > > large numbers.
> > > This means a domain may inadvertently set a cval so the result would
> > > overflow. Consequently, the deadline would be set very far in the
> > > future. This could result to loss of timer interrupts or the vCPU
> > > getting block "forever".
> > > One way to solve the problem, would be to separately
> > > 1) compute when the domain was created in ns
> > > 2) convert cval to ns
> > > 3) Add 1 and 2 together
> > > The first part of the equation never change (the value is set/known at
> > > domain creation). So take the opportunity to store it in domain structure.
> > > Signed-off-by: Jiamei Xie <jiamei.xie@xxxxxxx>
> > Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > The commit message is my own, I would like to Bertrand or Stefano to confirm 
> > they are happy with it :).
> I am ok with it so:
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
Thanks. I have committed the patch.

Cheers,

--
Julien Grall