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

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Message-ID: <20181030213557.GE10491@bombadil.infradead.org>
Date:   Tue, 30 Oct 2018 14:35:57 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Tycho Andersen <tycho@...ho.ws>,
        Andy Lutomirski <luto@...capital.net>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        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 Tue, Oct 30, 2018 at 10:43:14PM +0200, Igor Stoppa wrote:
> On 30/10/2018 21:20, Matthew Wilcox wrote:
> > > > So the API might look something like this:
> > > > 
> > > > 	void *p = rare_alloc(...);	/* writable pointer */
> > > > 	p->a = x;
> > > > 	q = rare_protect(p);		/* read-only pointer */
> 
> With pools and memory allocated from vmap_areas, I was able to say
> 
> protect(pool)
> 
> and that would do a swipe on all the pages currently in use.
> In the SELinux policyDB, for example, one doesn't really want to
> individually protect each allocation.
> 
> The loading phase happens usually at boot, when the system can be assumed to
> be sane (one might even preload a bare-bone set of rules from initramfs and
> then replace it later on, with the full blown set).
> 
> There is no need to process each of these tens of thousands allocations and
> initialization as write-rare.
> 
> Would it be possible to do the same here?

What Andy is proposing effectively puts all rare allocations into
one pool.  Although I suppose it could be generalised to multiple pools
... one mm_struct per pool.  Andy, what do you think to doing that?

> > but we'd probably wrap it in list_for_each_rare_entry(), just to be nicer.
> 
> This seems suspiciously close to the duplication of kernel interfaces that I
> was roasted for :-)

Can you not see the difference between adding one syntactic sugar function
and duplicating the entire infrastructure?