Date: Tue, 24 Apr 2007 17:21:46 -0400 From: John Baldwin <jhb@freebsd.org> To: src-committers@freebsd.org Cc: cvs-src@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/amd64/amd64 vm_machdep.c src/sys/i386/i386 vm_machdep.c Message-ID: <200704241721.46689.jhb@freebsd.org> In-Reply-To: <200704242117.l3OLHjRn017578@repoman.freebsd.org> References: <200704242117.l3OLHjRn017578@repoman.freebsd.org>
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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. -- John Baldwin
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