linux-kernel - Re: [PATCH 10/17] prmem: documentation

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Date:   Tue, 30 Oct 2018 11:03:51 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Andy Lutomirski <luto@...capital.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Igor Stoppa <igor.stoppa@...il.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Dave Chinner <david@...morbit.com>,
        James Morris <jmorris@...ei.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Igor Stoppa <igor.stoppa@...wei.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Laura Abbott <labbott@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 10/17] prmem: documentation

On 10/30/18 10:58 AM, Matthew Wilcox wrote:
> Does this satisfy Igor's requirements?  We wouldn't be able to
> copy_to/from_user() while rare_mm was active.  I think that's a feature
> though!  It certainly satisfies my interests (kernel code be able to
> mark things as dynamically-allocated-and-read-only-after-initialisation)

It has to be more than copy_to/from_user(), though, I think.

rare_modify(q) either has to preempt_disable(), or we need to teach the
context-switching code when and how to switch in/out of the rare_mm.
preempt_disable() would also keep us from sleeping.