linux-kernel - Re: [PATCH 2/5] lguest guest feedback tidyups

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Date:	Fri, 11 May 2007 17:31:06 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH 2/5] lguest guest feedback tidyups

On Fri, 2007-05-11 at 07:56 +0100, Christoph Hellwig wrote:
> On Fri, May 11, 2007 at 11:21:30AM +1000, Rusty Russell wrote:
> > 1) send-dma and bind-dma hypercall wrappers for drivers to use,
> > 2) formalization of the convention that devices can use the irq
> >    corresponding to their index on the lguest_bus.
> > 3) ___force to shut up sparse: guests *can* use ioremap as virtual mem.
> 
> No, they can't.  Even if in your case the underlying address spaces
> happen to be the same anything returned by ioremap must use the proper
> accessors.  That's the whole point of having this separation, otherwise
> you wouldn't need to use ioremap at all.

Hi Christoph!

	Well, without ioremap, the memory wouldn't normally be mapped.  Is
there something better to use?

> So instead of sprinkling cast
> around add lguest_read*/lguest_write* accessors that do the __force cast
> once and make sure the ioremap return value is always accessed using those.

And that's nothing to do with iremap.  They're required because guest
"physical" == host virtual, and casting a long to a "__user void *"
seems to require a __force.

I enjoy a good Hellwigging as much as anyone, but your aim is off.

Cheers,
Rusty.

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