• H. Peter Anvin's avatar
    x86-32: Start out cr0 clean, disable paging before modifying cr3/4 · 021ef050
    H. Peter Anvin authored
    Patch
    
      5a5a51db x86-32: Start out eflags and cr4 clean
    
    ... made x86-32 match x86-64 in that we initialize %eflags and %cr4
    from scratch.  This broke OLPC XO-1.5, because the XO enters the
    kernel with paging enabled, which the kernel doesn't expect.
    
    Since we no longer support 386 (the source of most of the variability
    in %cr0 configuration), we can simply match further x86-64 and
    initialize %cr0 to a fixed value -- the one variable part remaining in
    %cr0 is for FPU control, but all that is handled later on in
    initialization; in particular, configuring %cr0 as if the FPU is
    present until proven otherwise is correct and necessary for the probe
    to work.
    
    To deal with the XO case sanely, explicitly disable paging in %cr0
    before we muck with %cr3, %cr4 or EFER -- those operations are
    inherently unsafe with paging enabled.
    
    NOTE: There is still a lot of 386-related junk in head_32.S which we
    can and should get rid of, however, this is intended as a minimal fix
    whereas the cleanup can be deferred to the next merge window.
    Reported-by: default avatarAndres Salomon <dilinger@queued.net>
    Tested-by: default avatarDaniel Drake <dsd@laptop.org>
    Link: http://lkml.kernel.org/r/50FA0661.2060400@linux.intel.comSigned-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
    021ef050
head_32.S 18.3 KB