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Re: [Xen-devel] Re: [PATCH] infiniband/mthca : Fix userland mapping of m

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] infiniband/mthca : Fix userland mapping of mthca infiniband cards in Xen dom0
From: Roland Dreier <rdreier@xxxxxxxxx>
Date: Thu, 06 Jan 2011 10:51:57 -0800
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Cc: jackm@xxxxxxxxxxxxxx, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, rdreir@xxxxxxxxx, linux-rdma@xxxxxxxxxxxxxxx, Vivien Bernet-Rollande <vbr@xxxxxxxxxxx>, sean.hefty@xxxxxxxxx
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 > There is another way, which I hope can fix this issue (it fixes
 > the graphics drivers). Basically making the Xen MMU be aware of the E820
 > and consider any access to PFNs that are not in RAM to have VM_IO implicitly 
 > set.
 > The patches are at 
 > git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git
 > stable/p2m-identity.v4.3
 > And posted on LKML )https://lkml.org/lkml/2010/12/30/163)
 > They _should_ take care of your problem as long as the PFNs you
 > are mapping fall within the PCI BAR regions (which I would presume they
 > do since you are using ioremap).

Yes, that should work fine for all the cases I know of in the RDMA
drivers.  We are just mapping some PCI BAR space into userspace for
direct access to hardware (just like graphics, I think).

I definitely prefer a solution that doesn't require driver authors to
add a Xen-specific fix that isn't required on any other architecture.

 - R.

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