On 2020-11-08 01:56, Andrew Morton wrote: > On Sat, 7 Nov 2020 16:22:06 +0100 Stefan Agner <stefan@xxxxxxxx> wrote: > >> Most architectures define MAX_PHYSMEM_BITS in asm/sparsemem.h and don't >> include it in asm/pgtable.h. Include asm/sparsemem.h directly to get >> the MAX_PHYSMEM_BITS define on all architectures. >> >> This fixes a crash when accessing zram on 32-bit ARM platform with LPAE and >> more than 4GB of memory: >> Unable to handle kernel NULL pointer dereference at virtual address 00000000 > > Mysterious. Presumably without this include, some compilation unit is > picking up the wrong value of MAX_PHYSMEM_BITS? But I couldn't > actually see where/how this occurs. Can you please explain further? Not sure if I got that right, but from what I understand if MAX_PHYSMEM_BITS is not set in mm/zsmalloc.c it will set MAX_PHYSMEM_BITS to BITS_PER_LONG. And this is 32-bit, too short when LPAE is in use... -- Stefan
