linux-kernel - Re: [PATCH -mm -v4 1/3] i386/x86

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Message-Id: <200710090206.22383.nickpiggin@yahoo.com.au>
Date:	Tue, 9 Oct 2007 02:06:21 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	linux-mm@...ck.org, "H. Peter Anvin" <hpa@...or.com>,
	Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	akpm@...ux-foundation.org, Yinghai Lu <yhlu.kernel@...il.com>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm -v4 1/3] i386/x86_64 boot: setup data

On Tuesday 09 October 2007 18:22, Huang, Ying wrote:
> On Tue, 2007-10-09 at 01:25 +1000, Nick Piggin wrote:
> > On Tuesday 09 October 2007 16:40, Huang, Ying wrote:
> > > +unsigned long copy_from_phys(void *to, unsigned long from_phys,
> > > +			     unsigned long n)

> > I suppose that's not unreasonable to put in mm/memory.c, although
> > it's not really considered a problem to do this kind of stuff in
> > a low level arch file...
> >
> > You have no kernel virtual mapping for the source data?
>
> On 32-bit platform such as i386. Some memory zones have no kernel
> virtual mapping (highmem region etc).

I'm just wondering whether you really need to access highmem in
boot code...


> So I think this may be useful as a 
> universal way to access physical memory. But it can be more efficient to
> implement it in arch file for some arch. Should this implementation be
> used as a fall back implementation with attribute "weak"?

Definitely on most architectures it would just amount to
memcpy(dst, __va(phys), n);, right? However I don't know if
it's worth the trouble of overriding it unless there is some
non-__init user of it.
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