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 [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
