[PATCH 4/7] iommu/arm-smmu: Check for num_context_irqs > 0 to avoid divide by zero exception

[Will Deacon]

On Tue, Sep 24, 2013 at 04:06:58PM +0100, Andreas Herrmann wrote:
> With the right (or wrong;-) definition of v1 SMMU node in DTB it is
> possible to trigger a division by zero in arm_smmu_init_domain_context
> (if number of context irqs is 0):
> 
>        if (smmu->version == 1) {
>                root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
>  →             root_cfg->irptndx %= smmu->num_context_irqs;
>        } else {
> 
> Avoid this by checking for num_context_irqs > 0 before trying to
> assign interrupts to contexts.
> 
> Signed-off-by: Andreas Herrmann <andreas.herrmann at calxeda.com>
> ---
>  drivers/iommu/arm-smmu.c |   31 +++++++++++++++++--------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index f5a856e..0dfd255 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -828,21 +828,24 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  		return ret;
>  
>  	root_cfg->cbndx = ret;
> -	if (smmu->version == 1) {
> -		root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
> -		root_cfg->irptndx %= smmu->num_context_irqs;
> -	} else {
> -		root_cfg->irptndx = root_cfg->cbndx;
> -	}
>  
> -	irq = smmu->irqs[smmu->num_global_irqs + root_cfg->irptndx];
> -	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
> -			  "arm-smmu-context-fault", domain);
> -	if (IS_ERR_VALUE(ret)) {
> -		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
> -			root_cfg->irptndx, irq);
> -		root_cfg->irptndx = -1;
> -		goto out_free_context;
> +	if (smmu->num_context_irqs) {

Can we move this check to probe time, to avoid re-evaluating it every time
we initialise a new domain?

Will