Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR

[Kirill A. Shutemov]

On Thu, Jan 05, 2017 at 11:39:16AM -0800, Dave Hansen wrote:
> On 01/05/2017 11:29 AM, Kirill A. Shutemov wrote:
> > On Thu, Jan 05, 2017 at 11:13:57AM -0800, Dave Hansen wrote:
> >> On 12/26/2016 05:54 PM, Kirill A. Shutemov wrote:
> >>> MM would use min(RLIMIT_VADDR, TASK_SIZE) as upper limit of virtual
> >>> address available to map by userspace.
> >>
> >> What happens to existing mappings above the limit when this upper limit
> >> is dropped?
> > 
> > Nothing: we only prevent creating new mappings. All existing are not
> > affected.
> > 
> > The semantics here the same as with other resource limits.
> > 
> >> Similarly, why do we do with an application running with something
> >> incompatible with the larger address space that tries to raise the
> >> limit?  Say, legacy MPX.
> > 
> > It has to know what it does. Yes, it can change limit to the point where
> > application is unusable. But you can to the same with other limits.
> 
> I'm not sure I'm comfortable with this.  Do other rlimit changes cause
> silent data corruption?  I'm pretty sure doing this to MPX would.

Maybe it's too ugly, but MPX can set rlim_max to rlim_cur on enabling.

-- 
 Kirill A. Shutemov