On Tue, Mar 19, 2013 at 4:36 PM, Yu, Fenghua <fenghua...@intel.com> wrote: >> From: yhlu.ker...@gmail.com [mailto:yhlu.ker...@gmail.com] On Behalf Of >> Yinghai Lu >> On Tue, Mar 19, 2013 at 8:04 AM, Fenghua Yu <fenghua...@intel.com> >> wrote: >> > From: Fenghua Yu <fenghua...@intel.com> >> > >> > In 32-bit, __pa_symbol() in CONFIG_DEBUG_VIRTUAL accesses kernel data >> (e.g. >> > max_low_pfn) that haven't been setup yet in such early boot phase. To >> fix the >> > issue, __pa_nodebug() replaces __pa_symbol() to get a global symbol's >> physical >> > address. >> >> That explanation is not precise. >> >> __phys_addr in 32bit when DEBUG_VIRTUAL is set, it does have check >> /* max_low_pfn is set early, but not _that_ early */ >> if (max_low_pfn) { >> .... >> } >> the reason should be: >> in head_32.S, 32bit flat mode, you need to switch to phys addr to >> access >> global variable max_low_pfn. > > Max_low_pfn is not set up yet at this point, but __pa_symbol() reads it > if CONFIG_DEBUG_VIRTUAL. There is no need to access max_low_pfn or any > other data that is not setup yet if CONFIG_DEBUG_VIRTUAL. > > So I think the explanation is ok.
Changlog said: In 32-bit, __pa_symbol() in CONFIG_DEBUG_VIRTUAL accesses kernel data (e.g. max_low_pfn) that haven't been setup yet in such early boot phase. --- So do you mean we have to change all __pa_symbol before setup.c::setup_arch/find_low_pfn_range ? because only at that time max_low_pfn get setup. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
