On Wed, Feb 02, 2011 at 05:10:37PM -0500, Nicolas Pitre wrote: > On Wed, 2 Feb 2011, Russell King - ARM Linux wrote: > > > On Wed, Feb 02, 2011 at 03:43:29PM +0100, Per Fransson wrote: > > > When restarting using the kernel kexec functionality the MMU > > > needs to be turned off. Any code which does this needs to use > > > identity mapped addresses to get reliable results. In the ARM > > > kexec case this identity mapping is done: > > > > > > - using the page table of the current task > > > > > > - for all addresses normally used by user space, > > > i.e. 0x00000000-PAGE_OFFSET > > > > > > If kexec is used at a kernel crash to collect a core dump this > > > means that we lose important information. > > > > > > This is what this patches does: > > > > > > * Actually turns off the MMU, which has been omitted by mistake > > > > > > * Sets up a more selective identity mapping > > > > > > * Restores the old mapping once the MMU is off > > > > > > Signed-off-by: Per Fransson <per.xx.fransson at stericsson.com> > > > --- > > > v2 changes: > > > > > > * now uses (modified versions of) the identity mapping functions in idmap.c > > > as they look in 2.6.38-rc1. Some pud-level code has been added there in > > > linux-next. > > > > Thanks. As this been tested with ARMv4/v5 CPUs as well? > > I have doubts about the effectiveness of setup_mm_for_reboot() on any > machine where physical RAM starts at 0xc0000000 or above, such as on > SA1100. It's known to work on Assabet. It works on SA1100 because the kernel mapping is already a 1:1 mapping. What setup_mm_for_reboot() is doing on Assabet though is making the flash available for cpu_reset(0) to be able to call, not making the kernel code for cpu_reset() available for calling.
