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

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Date:	Tue, 28 Jul 2015 15:12:11 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Julien Grall <julien.grall@...rix.com>,
	xen-devel@...ts.xenproject.org
CC:	ian.campbell@...rix.com, stefano.stabellini@...citrix.com,
	linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Roger Pau Monné <roger.pau@...rix.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Wei Liu <wei.liu2@...rix.com>, Juergen Gross <jgross@...e.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	linux-input@...r.kernel.org, netdev@...r.kernel.org,
	linux-scsi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-fbdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/8] xen: Use the correctly the Xen memory terminologies

On 07/28/2015 11:02 AM, 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 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.




> @@ -730,7 +730,7 @@ static void xen_do_pin(unsigned level, unsigned long pfn)
>   	struct mmuext_op op;
>
>   	op.cmd = level;
> -	op.arg1.mfn = pfn_to_mfn(pfn);
> +	op.arg1.mfn = pfn_to_gfn(pfn);


This looks slightly odd. It is correct but given that purpose of this 
series is to make things more clear perhaps we can add another union 
member (gfn) to mmuext_op.arg1?

(Of course, the hypervisor will continue referring to mfn which could 
still be confusing)


>
>   	xen_extend_mmuext_op(&op);
>   }
> @@ -1323,7 +1323,7 @@ static void __xen_write_cr3(bool kernel, unsigned long cr3)
>   	trace_xen_mmu_write_cr3(kernel, cr3);
>
>   	if (cr3)
> -		mfn = pfn_to_mfn(PFN_DOWN(cr3));
> +		mfn = pfn_to_gfn(PFN_DOWN(cr3));

Here too. And further down, thoughout this patch.




-boris
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