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Date: Fri, 7 May 2010 14:49:01 +0800
Message-ID: <t2k2a27d3731005062349r4f12256bh7bffc6389b1dfcea@mail.gmail.com>
Subject: Re: Page fault on vmalloc'ed memory
From: Li Yang <leoli@freescale.com>
To: Paul Mackerras <paulus@samba.org>
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Cc: linuxppc-dev@ozlabs.org, Timur Tabi <timur.tabi@gmail.com>,
	Li Yang-R58472 <r58472@freescale.com>
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On Fri, May 7, 2010 at 1:38 PM, Paul Mackerras <paulus@samba.org> wrote:
> On Thu, May 06, 2010 at 12:28:44PM +0800, Li Yang wrote:
>
>> The root cause of this oops might not be related with the vmalloc'ed
>> area processing in Instruction Storage Interrupt. =C2=A0But x86 does hav=
e
>> the code for processing it while we don't. =C2=A0Is it because we have
>> nothing to do with the vmalloc'ed ISI on PowerPC architecture?
>
> On PowerPC we always read the kernel page tables rooted at
> swapper_pg_dir to get translations for kernel addresses (those above
> KERNELBASE). =C2=A0We can do that because it is kernel code (software) th=
at
> reads the Linux page tables. =C2=A0On x86, it is hardware that reads the
> Linux page tables, and it always reads the page tables for the current
> process. =C2=A0This means that the kernel part of each process's page
> tables needs to contain copies of all the kernel PTEs on x86. =C2=A0To
> avoid having to set a PTE in every process's page tables when doing a
> vmalloc or ioremap, x86 just creates them in swapper_pg_dir and then
> creates them on demand in each process's page tables as needed.
> That's why they have code to handle vmalloc faults in their page fault
> handler.

Thanks a lot for the explanation.

- Leo