linux-kernel - Re: [PATCH 1 of 3] add phys_addr_t for holding physical addresses

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Message-Id: <20080822143515.512ff182.akpm@linux-foundation.org>
Date:	Fri, 22 Aug 2008 14:35:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	ehabkost@...hat.com, benh@...nel.crashing.org, paulus@...ba.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1 of 3] add phys_addr_t for holding physical addresses

On Fri, 22 Aug 2008 14:11:16 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Andrew Morton wrote:
> > On Tue, 19 Aug 2008 13:02:50 -0700
> > Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> >
> >   
> >> Add a kernel-wide "phys_addr_t" which is guaranteed to be able to hold
> >> any physical address.  By default it equals the word size of the
> >> architecture, but a 32-bit architecture can set ARCH_PHYS_ADDR_T_64BIT
> >> if it needs a 64-bit phys_addr_t.
> >>
> >>     
> >
> > You say this is a bugfix but you don't describe the bug.  This makes it
> > rather hard to make the 2.6.2[5678] decisions.
> >
> > Ditto on [patch 2/3].
> >   
> 
> 1/3 is not a bugfix in itself, but a pre-requisite for 2/3.
> 
> 2/3 replaces an ad-hoc Xen fix with a general fix to prevent address
> truncation when using PFN_PHYS() on any PFN above the 4G mark.  The Xen
> crash is the only bug I know of that's directly attributable to this,
> and it was already addressed in older kernels with the casts in the Xen
> code that this patch removes.
> 
> So I don't think there's any strong need to push this to earlier kernels.
> 

Still confused.  The above implies that 2.6.27 doesn't need fixing
either, because the typecasts already avoid the crash.
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