linux-kernel - Re: [RFC PATCH 0/3] generic hypercall support

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Message-Id: <200905080011.52958.arnd@arndb.de>
Date:	Fri, 8 May 2009 00:11:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Gregory Haskins <gregory.haskins@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Anthony Liguori <anthony@...emonkey.ws>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC PATCH 0/3] generic hypercall support

On Thursday 07 May 2009, Chris Wright wrote:
> 
> > Chris, is that issue with the non ioread/iowrite access of a mangled
> > pointer still an issue here?  I would think so, but I am a bit fuzzy on
> > whether there is still an issue of non-wrapped MMIO ever occuring.
> 
> Arnd was saying it's a bug for other reasons, so perhaps it would work
> out fine.

Well, maybe. I only said that __raw_writel and pointer dereference is
bad, but not writel.

IIRC when we had that discussion about io-workarounds on powerpc,
the outcome was that passing an IORESOURCE_MEM resource into pci_iomap
must still result in something that can be passed into writel in addition
to iowrite32, while an IORESOURCE_IO resource may or may not be valid for
writel and/or outl.

Unfortunately, this means that either readl/writel needs to be adapted
in some way (e.g. the address also ioremapped to the mangled pointer)
or the mechanism will be limited to I/O space accesses.

Maybe BenH remembers the details better than me.

	Arnd <><
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