Messages in this thread Patch in this message | | | Date | Mon, 27 Nov 2006 15:16:46 -0800 | From | Jun Sun <> | Subject | Re: failed 'ljmp' in linear addressing mode |
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On Mon, Nov 27, 2006 at 08:58:57AM -0500, linux-os (Dick Johnson) wrote: > > I think it probably resets the instant that you turn off paging. To > turn off paging, you need to copy some code (properly linked) to an > area where there is a 1:1 mapping between virtual and physical addresses. > A safe place is somewhere below 1 megabyte. Then you need to set up a > call descriptor so you can call that code (you can ljump if you never > plan to get back). You then need to clear interrupts on all CPUs (use a > spin-lock). Once you are executing from the new area, you reset your > segments to the new area. The call descriptor would have already set > CS, as would have the long-jump. At this time you can turn off paging > and flush the TLB. You are now in linear-address protected mode. >
Thanks for the reply. But I am pretty much sure I did above correctly. I use single-instruction infinite loop in the call path to verify that control does reach last 'ljmp' but not the jump destination.
Below is the hack I made to machine_kexec.c file. As you can see, I managed to make the identical mapping between virtual and physical addresses.
Note I did not copy the code into the first 1M. In fact the code is located at 0xc0477000 (0x00477000 in physical). I thought that should be OK as I did not really go all the way back to real-address mode.
That last suspect I have now is the wrong value in CS descriptor. Does kernel have a suitable CS descriptor for the last ljmep to 0x10000000 in linear addressing mode? The CS descriptor seems to be a pretty dark magic to me ...
Cheers.
Jun
----------------- diff -Nru linux-2.6.17.14-1st/arch/i386/kernel/machine_kexec.c.orig linux-2.6.17.14-1st/arch/i386/kernel/machine_kexec.c --- linux-2.6.17.14-1st/arch/i386/kernel/machine_kexec.c.orig 2006-10-13 11:55:04.000000000 -0700 +++ linux-2.6.17.14-1st/arch/i386/kernel/machine_kexec.c 2006-11-22 15:01:45.000000000 -0800 @@ -212,3 +212,19 @@ rnk = (relocate_new_kernel_t) reboot_code_buffer; (*rnk)(page_list, reboot_code_buffer, image->start, cpu_has_pae); } + +extern void do_os_switching(void); +void os_switch(void) +{ + void (*foo)(void); + + /* absolutely no irq */ + local_irq_disable(); + + /* create identity mapping */ + foo=virt_to_phys(do_os_switching); + identity_map_page((unsigned long)foo); + + /* jump to the real address */ + foo(); +} - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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