Re: [PATCH v5 p2 01/19] xen/arm: Let the toolstack configure the number of SPIs

From: Julien Grall <julien.grall@citrix.com>
To: Ian Campbell <ian.campbell@citrix.com>,
	Julien Grall <julien.grall@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	tim@xen.org, Julien Grall <julien.grall@linaro.org>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	stefano.stabellini@citrix.com, Jan Beulich <jbeulich@suse.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v5 p2 01/19] xen/arm: Let the toolstack configure the number of SPIs
Date: Thu, 16 Apr 2015 16:10:07 +0100	[thread overview]
Message-ID: <552FD0CF.7050906@citrix.com> (raw)
In-Reply-To: <1429195179.25195.138.camel@citrix.com>

Hi Ian,

On 16/04/2015 15:39, Ian Campbell wrote:
> On Thu, 2015-04-09 at 16:09 +0100, Julien Grall wrote:
>> From: Julien Grall <julien.grall@linaro.org>
>>
>> Each domain may have a different number of IRQs depending on the devices
>> assigned to it.
>
>> Rather re-using the number of IRQs used by the hardwared GIC, let the
>
>           ^than
>
>> toolstack specify the number of SPIs when the domain is created. This
>> will avoid to waste memory.
>
>    "will avoid wasting memory."
>
>
>> +    /* Limit the number of virtual SPIs supported to (1020 - 32) = 988  */
>> +    if ( (nr_spis + NR_LOCAL_IRQS) > 1020 )
>> +        return -EINVAL;
>
> If there's any chance this can be called by not-completely trusted code
> (e.g. a disaggregated toolstack) then this if susceptible to an overflow
> (sorry, I gave you this code in a previous rev).

Hmmm, right.

> I think you can just move the NR_LOCAL_IRQS to the other side of the
> expression, i.e.
>      if ( nr_spis > 1020 - NR_LOCAL_IRQS )

I will do the change and adding a pair of parentheses for more clarity:

if ( nr_spis > (1020 - NR_LOCAL_IRQS) )

> With that and the grammar fixed:
> Acked-by: Ian Campbell <ian.campbell@citrix.com>

Thanks,

-- 
Julien Grall