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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: How to transfer memory from PCI memory directly to user space safely and portable?
Date: 27 Nov 2000 10:36:34 -0800
Organization: Transmeta Corporation, Santa Clara CA
Message-ID: <8vu9ji$r2a$1@cesium.transmeta.com>
In-Reply-To: <00112614213105.05228@paganini> <20001126151120.V2272@parcelfarce.linux.theplanet.co.uk>
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Followup to:  <20001126151120.V2272@parcelfarce.linux.theplanet.co.uk>
By author:    Philipp Rumpf <prumpf@parcelfarce.linux.theplanet.co.uk>
In newsgroup: linux.dev.kernel
> 
> I hope count isn't provided by userspace here ?
> 
> > 1. What happens if the user space memory is swapped to disk? Will 
> > verify_area() make sure that the memory is in physical RAM when it returns, 
> > or will it return -EFAULT, or will something even worse happen?
> 
> On i386, you'll sleep implicitly waiting for the page fault to be handled;  in
> the generic case, anything could happen.
> 

That doesn't sound right.  I would expect it to wait for the page to
be brought in on any and all architectures, otherwise it seems rather
impossible to write portable Linux kernel code.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt
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