From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: linuxppc-dev@ozlabs.org, monstr@monstr.eu,
Suzuki Poulose <suzuki@in.ibm.com>,
John Williams <john.williams@petalogix.com>
Subject: RE: Relocatable kernel for ppc44x
Date: Wed, 15 Jun 2011 20:14:36 +1000 [thread overview]
Message-ID: <1308132876.2516.3.camel@pasglop> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6D8AD9E@saturn3.aculab.com>
On Wed, 2011-06-15 at 10:30 +0100, David Laight wrote:
> > The PPC440X currently uses 256M TLB entries to pin the
> > lowmem. When we go for a relocatable kernel we have to :
> >
> > 1) Restrict the kernel load address to be 256M aligned
> >
> > OR
> >
> > 2) Use 16M TLB(the next possible TLB page size supported)
> > entries till the first
> > 256M and then use the 256M TLB entries for the rest of lowmem.
>
> What is wrong with:
>
> 3) Use 256M TLB entries with the lowest one including
> addresses below the kernel base.
>
> Clearly the kernel shouldn't be accessing the addresses
> below its base address - but that is true of a lot of
> address space mapped into the kernel.
In the case of a relocatable kernel it's perfectly kosher to access
addresses below the kernel itself... Typically this is used for kdump
where the kdump kernel excecutes in place in a reserved area but access
to the rest of memory is allowed to ... well, do the dump :-) There
could be other reasons to do that too.
Cheers,
Ben.
next prev parent reply other threads:[~2011-06-15 10:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-14 12:04 Relocatable kernel for ppc44x Michal Simek
2011-06-14 12:16 ` Josh Boyer
2011-06-15 6:13 ` Suzuki Poulose
2011-06-15 9:30 ` David Laight
2011-06-15 9:38 ` John Williams
2011-06-15 10:14 ` Benjamin Herrenschmidt [this message]
2011-06-15 10:11 ` Benjamin Herrenschmidt
2011-06-15 14:40 ` Suzuki Poulose
2011-06-15 16:02 ` Tirumala Marri
2011-06-15 19:47 ` Scott Wood
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