Re: [PATCH for 2.5] preemptible kernel

Nigel Gamble
2001-03-19T21:02:44Z

Hi Pavel,

Thanks for you comments.

On Sat, 17 Mar 2001, Pavel Machek wrote:
> > diff -Nur 2.4.2/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c
> > --- 2.4.2/arch/i386/kernel/traps.c Wed Mar 14 12:16:46 2001
> > +++ linux/arch/i386/kernel/traps.c Wed Mar 14 12:22:45 2001
> > @@ -973,7 +973,7 @@
> > set_trap_gate(11,&segment_not_present);
> > set_trap_gate(12,&stack_segment);
> > set_trap_gate(13,&general_protection);
> > - set_trap_gate(14,&page_fault);
> > + set_intr_gate(14,&page_fault);
> > set_trap_gate(15,&spurious_interrupt_bug);
> > set_trap_gate(16,&coprocessor_error);
> > set_trap_gate(17,&alignment_check);
>
> Are you sure about this piece? Add least add a comment, because it
> *looks* strange.

With a preemptible kernel, we need to enter the page fault handler with
interrupts disabled to protect the cr2 register. The interrupt state is
restored immediately after cr2 has been saved. Otherwise, an interrupt
could cause the faulting thread to be preempted, and the new thread
could also fault, clobbering the cr2 register for the preempted thread.
See the diff for linux/arch/i386/mm/fault.c.

Nigel Gamble nigel@nrg.org
Mountain View, CA, USA. http://www.nrg.org/

MontaVista Software nigel@mvista.com