linux-kernel - Re: [Xen-devel] [PATCH 4/8] xen: Use the correctly the Xen memory terminologies

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Message-ID: <55B7B8D2.5060107@citrix.com>
Date:	Tue, 28 Jul 2015 18:16:02 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-fbdev@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
	"Jiri Slaby" <jslaby@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	<stefano.stabellini@...citrix.com>,
	Russell King <linux@....linux.org.uk>,
	<linux-scsi@...r.kernel.org>, <x86@...nel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	<linux-input@...r.kernel.org>,
	"Jean-Christophe Plagniol-Villard" <plagnioj@...osoft.com>,
	<ian.campbell@...rix.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Ingo Molnar <mingo@...hat.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Juergen Gross <jgross@...e.com>,
	"Wei Liu" <wei.liu2@...rix.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	<linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	<netdev@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	Roger Pau Monné 
	<roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH 4/8] xen: Use the correctly the Xen memory
 terminologies

On 28/07/15 16:02, Julien Grall wrote:
> Based on include/xen/mm.h [1], Linux is mistakenly using MFN when GFN
> is meant, I suspect this is because the first support for Xen was for
> PV. This brough some misimplementation of helpers on ARM and make the
> developper confused the expected behavior.

For the benefit of other subsystem maintainers, this is a purely
mechanical change in Xen-specific terminology.  It doesn't need reviews
or acks from non-Xen people (IMO).

> For instance, with pfn_to_mfn, we expect to get an MFN based on the name.
> Although, if we look at the implementation on x86, it's returning a GFN.
> 
> For clarity and avoid new confusion, replace any reference of mfn into
> gnf in any helpers used by PV drivers.
> 
> Take also the opportunity to simplify simple construction such
> as pfn_to_mfn(page_to_pfn(page)) into page_to_gfn. More complex clean up
> will come in follow-up patches.
> 
> I think it may be possible to do further clean up in the x86 code to
> ensure that helpers returning machine address (such as virt_address) is
> not used by no auto-translated guests. I will let x86 xen expert doing
> it.

Reviewed-by: David Vrabel <david.vrabel@...rix.com>

It looks a bit odd to use GFN in some of the PV code where the
hypervisor API uses MFN but overall I think using the correct
terminology where possible is best.  But I'd like to have Boris's or
Konrad's opinion on this.

David
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