Re: x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt

[Andi Kleen]

On Wed, Nov 30, 2005 at 08:03:33PM -0800, Zwane Mwaikambo wrote:
> NULL dereferences don't cause a page fault if the 4th level pagetable 
> being used is init_level4_pgt because we never zap_low_mappings. Since 
> the idle thread uses init_level4_pgt any bad dereferences happening there 
> (e.g. from interrupts) won't cause a fault. Andi would you be fine with 
> switching the idle threads to a different level4?

That recently changed. Are you sure it's still the case?

idle threads should always run with lazy TLB, no different mms.
That's important for performance.

If a NULL reference causes a oops or not depends on if user space
from the last process mapped a page to NULL or not.

-Andi
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