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

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Date:	Tue, 21 Jun 2016 14:56:17 +0200
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Yigal Korman <yigal@...xistor.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-nvdimm@...ts.01.org
Subject: Re: [PATCH] x86/mm: only allow memmap=XX!YY over existing RAM

On Mon, Jun 20, 2016 at 10:33:59AM +0300, Yigal Korman 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: Johannes Thumshirn <jthumshirn@...e.de>

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