linux-kernel - Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM

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Message-ID: <CAPcyv4gmK9ZJi3gFCqAOa2gLd2Nf1rwv_S1GC2nN-8mQBFspFA@mail.gmail.com>
Date:	Mon, 20 Jun 2016 07:44:18 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Yigal Korman <yigal@...xistor.com>
Cc:	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>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	jmoyer <jmoyer@...hat.com>, Toshi Kani <toshi.kani@....com>
Subject: Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM

On Mon, Jun 20, 2016 at 12:33 AM, Yigal Korman <yigal@...xistor.com> wrote:
> Before this patch, passing a range that is beyond the physical memory
> range will succeed, the user will see a /dev/pmem0 and will be able to
> access it. Reads will always return 0 and writes will be silently
> ignored.
>
> I've gotten more than one bug report about mkfs.{xfs,ext4} or nvml
> failing that were eventually tracked down to be wrong values passed to
> memmap.
>
> This patch prevents the above issue by instead of adding a new memory
> range, only update a RAM memory range with the PRAM type. This way,
> passing the wrong memmap will either not give you a pmem at all or give
> you a smaller one that actually has RAM behind it.
>
> And if someone still needs to fake a pmem that doesn't have RAM behind
> it, they can simply do memmap=XX@YY,XX!YY.
>
> Signed-off-by: Yigal Korman <yigal@...xistor.com>

Acked-by: Dan Williams <dan.j.williams@...el.com>