linux-kernel - Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function

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Message-ID: <92e56b28-0cd4-e3f4-867b-639d9b98b86c@intel.com>
Date:   Mon, 10 Jun 2019 15:02:45 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Andy Lutomirski <luto@...capital.net>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup
 function

On 6/10/19 1:58 PM, Yu-cheng Yu wrote:
>>> On each memory request, the kernel then must consider a percentage of
>>> allocated space in its calculation, and on systems with less memory
>>> this quickly becomes a problem.
>> I'm not sure what you're referring to here?  Are you referring to our
>> overcommit limits?
> Yes.

My assumption has always been that these large, potentially sparse
hardware tables *must* be mmap()'d with MAP_NORESERVE specified.  That
should keep them from being problematic with respect to overcommit.