Re: [Xen-devel] [PATCH v2 for-4.10] x86/mm: Make PV linear pagetables optional

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.10.17 at 15:49, <george.dunlap@xxxxxxxxxx> wrote:
> On 10/18/2017 02:41 PM, Jan Beulich wrote:
>>>>> On 18.10.17 at 12:51, <george.dunlap@xxxxxxxxxx> wrote:
>>> @@ -2334,6 +2368,9 @@ static int _put_page_type(struct page_info *page, 
>>> bool preemptible,
>>>                  ASSERT(ptpg->linear_pt_count > 0);
>>>                  ptpg = NULL;
>>>              }
>>> +#else /* CONFIG_PV_LINEAR_PT */
>>> +            BUG_ON(ptpg && PGT_type_equal(x, ptpg->u.inuse.type_info));
>>> +#endif
>> 
>> Along the lines of my most recent reply to v1 (which I realize I
>> did send only after v2 had arrived), I'm not really certain about
>> the usefulness of the preprocessor conditionals - I'd prefer if
>> we went without them, but I can live with them if you strongly
>> think they're better than the alternative. If you keep them,
>> please convert the BUG_ON() to ASSERT() though, to be in
>> line with the #ifdef side.
> 
> I would argue that if linear pagetables are disabled, and we nonetheless
> detect a linear pagetable, then BUG_ON() is the right behavior.  Since
> we're not properly tracking any of it, it is almost certainly the result
> of a security vulnerability.  Having a DoS in that case is much
> preferrable to having a privilege escalation.

Okay, I can accept that argument. Which means, with the formatting
issue in Kconfig taken care of,
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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