cvs commit: src/sys/amd64/amd64 vm_machdep.c src/sys/i386/i386 vm_machdep.c

Kris Kennaway kris at
Tue Apr 24 21:29:29 UTC 2007

On Tue, Apr 24, 2007 at 05:21:46PM -0400, John Baldwin wrote:
> On Tuesday 24 April 2007 05:17:45 pm John Baldwin wrote:
> > jhb         2007-04-24 21:17:45 UTC
> > 
> >   FreeBSD src repository
> > 
> >   Modified files:
> >     sys/amd64/amd64      vm_machdep.c 
> >     sys/i386/i386        vm_machdep.c 
> >   Log:
> >   Fix the triple fault used as a last resort during a reboot to actually
> >   fault.  The previous method zero'd out the page tables, invalidated the
> >   TLB, and then entered a spin loop.  The idea was that the instruction 
> after
> >   the TLB invalidate would result in a page fault and the page fault and
> >   subsequent double fault wouldn't be able to determine the physical page
> >   for their fault handlers' first instruction.  This stopped working when
> >   PGE (PG_G PTE/PDE bit) support was added as a TLB invalidate via %cr3
> >   reload doesn't clear TLB entries with PG_G set.  Thus, the CPU was still
> >   able to map the virtual address for the spin loop and happily performed
> >   its infinite loop.
> >   
> >   The triple fault now uses a much more deterministic sledge-hammer approach
> >   to generate a triple fault.  First, the IDT descriptor is set to point to
> >   an empty IDT, so any interrupts (including a double fault) will instantly
> >   fault.  Second, we trigger a int 3 breakpoint to force an interrupt and
> >   kick off a triple fault.
> >   
> >   MFC after:      3 days
> This and the other changes to support more methods for kicking off a reset 
> might fix problems people have with machines not rebooting but just hanging.  
> IIRC, there was a problem on some Dell 1950s that wouldn't reboot properly, 
> so they might be a good candidate for this.  I ran into this at work on a 
> machine that didn't have a functional keyboard controller, so it didn't 
> reboot when the keyboard reset failed, but just hung.

Some of my newer machines sometimes fail to reboot without power
cycling, so I'll keep an eye out.


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