Re: [Xen-devel] [PATCH v3 1/2] gnttab: don't use possibly unbounded tail calls

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 16/08/17 10:52, Jan Beulich wrote:
>>>> On 15.08.17 at 17:04, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 15/08/17 14:49, Jan Beulich wrote:
>>> @@ -2608,7 +2610,7 @@ static long gnttab_copy(
>>>      {
>>>          if ( i && hypercall_preempt_check() )
>>>          {
>>> -            rc = i;
>>> +            rc = count - i;
>> Somewhere, probably as a comment for gnttab_copy(), we should have a
>> comment explaining why the return value is different from all other ops,
>> which will also go somewhat to explaining the "rc = count - rc;" logic.
> Sure.
>
>> I think it would also be wise to have an early exit in
>> do_grant_table_op() for passing a count of 0.  As far as I can tell, we
>> will get all the way into the subop handler before discovering a count of 0.
> Well, that would collide with {get,set}_version which don't currently
> honor count (and hence existing callers may be passing zero here).
> Otherwise I would agree with what you propose.

Lovely :(

We've also got a number of other issues, like the fact that count, being
unsigned int, gets silently truncated in the non-compat case.

~Andrew

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