linux-kernel - Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT

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Message-ID: <20170105201153.GA27928@node.shutemov.name>
Date:   Thu, 5 Jan 2017 23:11:53 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [RFC, PATCHv2 29/29] mm, x86: introduce RLIMIT_VADDR

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