Re: [PATCH v3 1/7] xen/gnttab: Rework resource acquisition

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.01.2021 17:03, Andrew Cooper wrote:
> On 15/01/2021 11:43, Jan Beulich wrote:
>>> +    mfn_t tmp;
>>> +    void **vaddrs;
>>> +    int rc;
>>> +
>>> +    /* Overflow checks */
>>> +    if ( frame + nr_frames < frame )
>>> +        return -EINVAL;
>>> +
>>> +    tot_frames = frame + nr_frames;
>>> +    if ( tot_frames != frame + nr_frames )
>>> +        return -EINVAL;
>> Can't these two be folded into
>>
>>     unsigned int tot_frames = frame + nr_frames;
>>
>>     if ( tot_frames < frame )
>>         return -EINVAL;
>>
>> ? Both truncation and wrapping look to be taken care of this
>> way.
> 
> Not when frame is a multiple of 4G (or fractionally over, I think).

How that? In this case any unsigned int value will be less than
frame.

Jan