linux-kernel - Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA

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Message-ID: <20150813144132.GC17375@lst.de>
Date:	Thu, 13 Aug 2015 16:41:32 +0200
From:	Christoph Hellwig <hch@....de>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Rik van Riel <riel@...hat.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux MM <linux-mm@...ck.org>, Mel Gorman <mgorman@...e.de>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into
	KVA

On Thu, Aug 13, 2015 at 04:23:38PM +0300, Boaz Harrosh wrote:
> > DAX as is is races against pmem unbind.   A synchronization cost must
> > be paid somewhere to make sure the memremap() mapping is still valid.
> 
> Sorry for being so slow, is what I asked. what is exactly "pmem unbind" ?
> 
> Currently in my 4.1 Kernel the ioremap is done on modprobe time and
> released modprobe --remove time. the --remove can not happen with a mounted
> FS dax or not. So what is exactly "pmem unbind". And if there is a new knob
> then make it refuse with a raised refcount.

Surprise removal of a PCIe card which is mapped to provide non-volatile
memory for example.  Or memory hot swap.
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