* x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt
@ 2005-12-01 4:03 Zwane Mwaikambo
2005-12-01 13:18 ` Andi Kleen
0 siblings, 1 reply; 3+ messages in thread
From: Zwane Mwaikambo @ 2005-12-01 4:03 UTC (permalink / raw)
To: Linux Kernel; +Cc: Andi Kleen, Andrew Morton, William Lee Irwin III, Raj, Ashok
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?
Thanks,
Zwane
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt
2005-12-01 4:03 x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt Zwane Mwaikambo
@ 2005-12-01 13:18 ` Andi Kleen
2005-12-01 19:34 ` Zwane Mwaikambo
0 siblings, 1 reply; 3+ messages in thread
From: Andi Kleen @ 2005-12-01 13:18 UTC (permalink / raw)
To: Zwane Mwaikambo
Cc: Linux Kernel, Andi Kleen, Andrew Morton, William Lee Irwin III,
Raj, Ashok
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt
2005-12-01 13:18 ` Andi Kleen
@ 2005-12-01 19:34 ` Zwane Mwaikambo
0 siblings, 0 replies; 3+ messages in thread
From: Zwane Mwaikambo @ 2005-12-01 19:34 UTC (permalink / raw)
To: Andi Kleen; +Cc: Linux Kernel, Andrew Morton, William Lee Irwin III, Raj, Ashok
On Thu, 1 Dec 2005, Andi Kleen wrote:
> 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.
Ah thanks Andi, yes NULL reference causes an oops in the current -git
repository, i hadn't seen that change so i had last tested it on 2.6.13.
Sorry for the noise.
Zwane
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2005-12-01 19:28 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2005-12-01 4:03 x86_64/HOTPLUG_CPU: NULL dereference doesn't #PF with init_level4_pgt Zwane Mwaikambo
2005-12-01 13:18 ` Andi Kleen
2005-12-01 19:34 ` Zwane Mwaikambo
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