linux-kernel - Re: [PATCH 1/8] arm/xen: Remove helpers which are PV specific

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Date:	Fri, 31 Jul 2015 11:55:42 +0100
From:	Ian Campbell <ian.campbell@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Julien Grall <julien.grall@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	"Russell King" <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/8] arm/xen: Remove helpers which are PV specific

On Fri, 2015-07-31 at 11:44 +0100, Stefano Stabellini wrote:
> On Tue, 28 Jul 2015, Julien Grall wrote:
> > ARM guests are assimilated to HVM guest on ARM. The current
> > implementation is assuming a 1:1 mapping which is only true for DOM0 
> > and
> > may not be at all in the future.
> > 
> > Furthermore, all the helpers but arbitrary_virt_to_machine are used in
> > x86 specific code (or only compiled for).
> > 
> > The helper arbitrary_virt_to_machine is only used in PV specific code.
> > Therefore we should never call the function.
> > 
> > Add a BUG() in this helper and drop all the others.
> > 
> > Signed-off-by: Julien Grall <julien.grall@...rix.com>
> > Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > Cc: Russell King <linux@....linux.org.uk>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > ---
> >  arch/arm/include/asm/xen/page.h | 16 ++--------------
> >  1 file changed, 2 insertions(+), 14 deletions(-)
> > 
> > diff --git a/arch/arm/include/asm/xen/page.h 
> > b/arch/arm/include/asm/xen/page.h
> > index 1bee8ca..c2e9dcd 100644
> > --- a/arch/arm/include/asm/xen/page.h
> > +++ b/arch/arm/include/asm/xen/page.h
> > @@ -54,26 +54,14 @@ static inline unsigned long mfn_to_pfn(unsigned 
> > long mfn)
> >  
> >  #define mfn_to_local_pfn(mfn) mfn_to_pfn(mfn)
> >  
> > -static inline xmaddr_t phys_to_machine(xpaddr_t phys)
> > -{
> > -	unsigned offset = phys.paddr & ~PAGE_MASK;
> > -	return XMADDR(PFN_PHYS(pfn_to_mfn(PFN_DOWN(phys.paddr))) | 
> > offset);
> > -}
> > -
> > -static inline xpaddr_t machine_to_phys(xmaddr_t machine)
> > -{
> > -	unsigned offset = machine.maddr & ~PAGE_MASK;
> > -	return XPADDR(PFN_PHYS(mfn_to_pfn(PFN_DOWN(machine.maddr))) | 
> > offset);
> > -}
> >  /* VIRT <-> MACHINE conversion */
> > -#define virt_to_machine(v)	(phys_to_machine(XPADDR(__pa(v))))
> >  #define virt_to_mfn(v)		(pfn_to_mfn(virt_to_pfn(v)))
> >  #define mfn_to_virt(m)		(__va(mfn_to_pfn(m) << PAGE_SHIFT))
> >  
> > +/* Only used in PV code. However ARM guest is always assimilated as 
> > HVM. */
>                                ^ "However" doesn't make sense here from an
>                                english grammer point of view.

"English grammar" :-P

Sorry. What I really meant to say was that "assimilated" doesn't make sense
in this context either. I think maybe what was meant is "ARM guests are
always HVM".

Ian.
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