Re: [Xen-devel] [PATCH v2] psr: fix bug which may cause crash

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.11.2019 02:41, Yi Sun wrote:
> On 19-11-28 12:25:44, Jan Beulich wrote:
>> On 28.11.2019 11:18, Yi Sun wrote:
>>> --- a/xen/arch/x86/psr.c
>>> +++ b/xen/arch/x86/psr.c
>>> @@ -1271,7 +1271,8 @@ static void do_write_psr_msrs(void *data)
>>>  
>>>          for ( j = 0; j < cos_num; j++, index++ )
>>>          {
>>> -            if ( feat->cos_reg_val[cos * cos_num + j] != info->val[index] )
>>> +            if ( cos <= feat->cos_max &&
>>> +                 feat->cos_reg_val[cos * cos_num + j] != info->val[index] )
>>
>> The description is indeed much better now, thanks. However,
>> as indicated in reply to v1, this extra (and at the first glance
>> unmotivated) bounds check wants to be accompanied by a brief but
> 
> I will add the comment.
> 
>> precise comment. Furthermore with the loop bounded by a local
>> variable, why not
>>
>>         cos_num = min(props->cos_num, feat->cos_max + 1);
>>
>> a few lines up from here (again suitable commented)?
>>
> cos_num is a different thing with the number of COS registers. The
> meaning of it is "COS registers number that feature uses for one COS
> ID". E.g. MBA/CAT cos_num is always 1. But CDP cos_num is 2 because it
> uses 2 COS registers for one COS ID.

Oh, right, I got confused. The cos <= feat->cos_max is entirely
loop invariant. Hence the loop shouldn't even be entered, i.e.
you want to add a conditional ahead of it.

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel