• Ard Biesheuvel's avatar
    arm64: mm: use single quantity to represent the PA to VA translation · 7bc1a0f9
    Ard Biesheuvel authored
    On arm64, the global variable memstart_addr represents the physical
    address of PAGE_OFFSET, and so physical to virtual translations or
    vice versa used to come down to simple additions or subtractions
    involving the values of PAGE_OFFSET and memstart_addr.
    
    When support for 52-bit virtual addressing was introduced, we had to
    deal with PAGE_OFFSET potentially being outside of the region that
    can be covered by the virtual range (as the 52-bit VA capable build
    needs to be able to run on systems that are only 48-bit VA capable),
    and for this reason, another translation was introduced, and recorded
    in the global variable physvirt_offset.
    
    However, if we go back to the original definition of memstart_addr,
    i.e., the physical address of PAGE_OFFSET, it turns out that there is
    no need for two separate translations: instead, we can simply subtract
    the size of the unaddressable VA space from memstart_addr to make the
    available physical memory appear in the 48-bit addressable VA region.
    
    This simplifies things, but also fixes a bug on KASLR builds, which
    may update memstart_addr later on in arm64_memblock_init(), but fails
    to update vmemmap and physvirt_offset accordingly.
    
    Fixes: 5383cc6e ("arm64: mm: Introduce vabits_actual")
    Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
    Reviewed-by: default avatarSteve Capper <steve.capper@arm.com>
    Link: https://lore.kernel.org/r/20201008153602.9467-2-ardb@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
    7bc1a0f9
memory.h 10.6 KB