On 02/26/2020 08:14 PM, Christophe Leroy wrote: > > > Le 26/02/2020 à 15:12, Qian Cai a écrit : >> On Wed, 2020-02-26 at 09:09 -0500, Qian Cai wrote: >>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote: >>> >>> How useful is this that straightly crash the powerpc? >> >> And then generate warnings on arm64, >> >> [ 146.634626][ T1] debug_vm_pgtable: debug_vm_pgtable: Validating >> architecture page table helpers >> [ 146.643995][ T1] ------------[ cut here ]------------ >> [ 146.649350][ T1] virt_to_phys used for non-linear address: >> (____ptrval____) (start_kernel+0x0/0x580) > > Must be something wrong with the following in debug_vm_pgtable() > > paddr = __pa(&start_kernel); > > Is there any explaination why start_kernel() is not in linear memory on ARM64 ? Cc: + James Morse <james.morse@xxxxxxx> This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol i.e 'start_kernel' which might be outside the linear map. This happens due to kernel mapping position randomization with KASLR. Adding James here in case he might like to add more. __pa_symbol() should have been used instead, for accessing the physical address here. On arm64 __pa() does check for linear address with __is_lm_address() and switch accordingly if it is a kernel text symbol. Nevertheless, its much better to use __pa_symbol() here rather than __pa(). Rather than respining the patch once more, will just send a fix replacing this helper __pa() with __pa_symbol() for Andrew to pick up as this patch is already part of linux-next (next-20200226). But can definitely respin if that will be preferred. Thanks Qian for catching this. > > Christophe >
