Re: [Xen-devel] [PATCH v6 1/2] arm: remove irq from inflight, then change physical affinity

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 04/04/17 02:09, Stefano Stabellini wrote:
> This patch fixes a potential race that could happen when
> gic_update_one_lr and vgic_vcpu_inject_irq run simultaneously.
>
> When GIC_IRQ_GUEST_MIGRATING is set, we must make sure that the irq has
> been removed from inflight before changing physical affinity, to avoid
> concurrent accesses to p->inflight, as vgic_vcpu_inject_irq will take a
> different vcpu lock.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> ---
>  xen/arch/arm/gic.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> index 9522c6c..de996d9 100644
> --- a/xen/arch/arm/gic.c
> +++ b/xen/arch/arm/gic.c
> @@ -503,6 +503,11 @@ static void gic_update_one_lr(struct vcpu *v, int i)
>              gic_raise_guest_irq(v, irq, p->priority);
>          else {
>              list_del_init(&p->inflight);
> +            /* Remove from inflight, then change physical affinity. It
> +             * makes sure that when a new interrupt is received on the
> +             * next pcpu, inflight is already cleared. No concurrent
> +             * accesses to inflight. */
Coding style:

/*
 * ...
 */

With that:

Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

> +            smp_wmb();
>              if ( test_and_clear_bit(GIC_IRQ_GUEST_MIGRATING, &p->status) )
>              {
>                  struct vcpu *v_target = vgic_get_target_vcpu(v, irq);
Cheers,

--
Julien Grall

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