linux-kernel - Re: [PATCH] x86: fix kaslr and memmap collision

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Date:   Thu, 24 Nov 2016 11:04:58 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH] x86: fix kaslr and memmap collision

On Tue, Nov 22, 2016 at 11:01:32AM -0800, Dan Williams wrote:
> On Tue, Nov 22, 2016 at 10:54 AM, Kees Cook <keescook@...omium.org> wrote:
> > On Tue, Nov 22, 2016 at 9:26 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> >> No, you're right, we need to handle multiple ranges.  Since the
> >> mem_avoid array is statically allocated perhaps we can handle up to 4
> >> memmap= entries, but past that point disable kaslr for that boot?
> >
> > Yeah, that seems fine to me. I assume it's rare to have 4?
> >
> 
> It should be rare to have *one* since ACPI 6.0 added support for
> communicating persistent memory ranges.  However there are legacy
> nvdimm users that I know are doing at least 2, but I have hard time
> imagining they would ever do more than 4.

I doubt it's rare amongst the people using RAM to emulate pmem for
filesystem testing purposes. My "pmem" test VM always has at least 2
ranges set to give me two discrete pmem devices, and I have used 4
from time to time to do things like test multi-volume scratch XFS
filesystems in xfstests (i.e. data, log and realtime volumes) so I
didn't need to play games with partitioning or DM...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com