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Date: Thu, 21 Mar 2013 11:57:32 -0600
From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
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Subject: Re: [Qemu-devel] [PATCH] rdma: don't make pages writeable if not
	requiested
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Roland Dreier <roland@kernel.org>, qemu-devel@nongnu.org, "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>, Yishai Hadas <yishaih@mellanox.com>, LKML <linux-kernel@vger.kernel.org>, "Michael R. Hines" <mrhines@linux.vnet.ibm.com>, Hal Rosenstock <hal.rosenstock@gmail.com>, Sean Hefty <sean.hefty@intel.com>, Christoph Lameter <cl@linux.com>

On Thu, Mar 21, 2013 at 07:42:37PM +0200, Michael S. Tsirkin wrote:

> It doesn't actually, and our app would sometimes write to these pages.
> It simply does not care which version does the remote get in this case
> since we track writes and resend later.

Heh, somehow I thought you might say that :)

A new flag seems like the only way then - maybe:
  IBV_ACCESS_NON_COHERENT - The adaptor and the CPU do not share
     a coherent view of registered memory. Memory writes from the CPU
     after ibv_reg_mr completes may not be reflected in the memory
     viewed by the adaptor.

     Can only be combined with read only access permissions.

Jason