Page fault on vmalloc'ed memory

[Li Yang]

On Fri, May 7, 2010 at 1:38 PM, Paul Mackerras <paulus at 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.  But x86 does have
>> the code for processing it while we don't.  Is 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).  We can do that because it is kernel code (software) that
> reads the Linux page tables.  On x86, it is hardware that reads the
> Linux page tables, and it always reads the page tables for the current
> process.  This means that the kernel part of each process's page
> tables needs to contain copies of all the kernel PTEs on x86.  To
> 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