linux-kernel - Re: [PATCH RFC V2 12/17] memremap: Add zone device access protection

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Message-ID: <20200717092014.GB10769@hirez.programming.kicks-ass.net>
Date:   Fri, 17 Jul 2020 11:20:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     ira.weiny@...el.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V2 12/17] memremap: Add zone device access protection

On Fri, Jul 17, 2020 at 12:20:51AM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Device managed memory exposes itself to the kernel direct map which
> allows stray pointers to access these device memories.
> 
> Stray pointers to normal memory may result in a crash or other
> undesirable behavior which, while unfortunate, are usually recoverable
> with a reboot.  Stray writes to areas such as non-volatile memory are
> permanent in nature and thus are more likely to result in permanent user
> data loss vs a stray write to other memory areas

> +		pks_update_protection(dev_page_pkey, PKEY_DISABLE_ACCESS);

So on the one hand you talk about the problem of stray writes, but then
you disable all access.