• Helge Deller's avatar
    parisc: fix usage of 32bit PTE page table entries on 32bit kernels · 48d27cb2
    Helge Deller authored
    This patch fixes a long outstanding bug on 32bit parisc linux kernels
    which prevented us from using 32bit PTE table entries (instead of 64bit
    entries of which 32bit were unused).
    
    The problem was caused by this assembler statement in the L2_ptep
    macro in arch/parisc/kernel/entry.S:447:
    	EXTR \va,31-ASM_PGDIR_SHIFT,ASM_BITS_PER_PGD,\index
    which expanded to
    	extrw,u r8,9,11,r1
    and which has undefined behavior since the length value (11) extends
    beyond the leftmost bit (11-1 > 9).
    Interestingly PA2.0 processors seem to don't care and just zero-extend
    the value, while PA1.1 processors don't.
    
    Fix this problem by detecting an address space overflow with ASM_BITS_PER_PGD
    and adjusting it accordingly. To prevent such problems in the future,
    some compile time sanity checks in arch/parisc/mm/init.c were added.
    
    Since the page table now only consumes half of it's old size, we can
    use the freed memory to harmonize 32- and 64bit kernels and let both
    map 16MB for the initial page table.
    Signed-off-by: default avatarHelge Deller <deller@gmx.de>
    Signed-off-by: default avatarKyle McMartin <kyle@mcmartin.ca>
    48d27cb2
page.h 4.56 KB