Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

[Vlastimil Babka]

On 1/18/19 5:49 AM, Linus Torvalds wrote:
> On Fri, Jan 18, 2019 at 9:45 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>>
>> Or maybe we could resort to the 5.0-rc1 page table check (that is now being
>> reverted) but only in cases when we are not allowed the page cache residency
>> check? Or would that be needlessly complicated?
> 
> I think it would  be good fallback semantics, but I'm not sure it's
> worth it. Have you tried writing a patch for it? I don't think you'd
> want to do the check *when* you find a hole, so you'd have to do it
> upfront and then pass the cached data down with the private pointer
> (or have a separate "struct mm_walk" structure, perhaps?
> 
> So I suspect we're better off with the patch we have. But if somebody
> *wants* to try to do that fancier patch, and it doesn't look
> horrendous, I think it might be the "quality" solution.

I thought to drop the idea because of leaking that page has been
evicted, but then I realized there are other ways to check for that
anyway in /proc. So I'll try, but probably not until after next week. If
somebody else wants to, they are welcome. As you say, the current
solution should be ok, so that would be a patch on top anyway, for
bisectability etc.

Vlastimil

>               Linus
>