• Tejun Heo's avatar
    x86: fold pda into percpu area on SMP · 1a51e3a0
    Tejun Heo authored
    [ Based on original patch from Christoph Lameter and Mike Travis. ]
    
    Currently pdas and percpu areas are allocated separately.  %gs points
    to local pda and percpu area can be reached using pda->data_offset.
    This patch folds pda into percpu area.
    
    Due to strange gcc requirement, pda needs to be at the beginning of
    the percpu area so that pda->stack_canary is at %gs:40.  To achieve
    this, a new percpu output section macro - PERCPU_VADDR_PREALLOC() - is
    added and used to reserve pda sized chunk at the start of the percpu
    area.
    
    After this change, for boot cpu, %gs first points to pda in the
    data.init area and later during setup_per_cpu_areas() gets updated to
    point to the actual pda.  This means that setup_per_cpu_areas() need
    to reload %gs for CPU0 while clearing pda area for other cpus as cpu0
    already has modified it when control reaches setup_per_cpu_areas().
    
    This patch also removes now unnecessary get_local_pda() and its call
    sites.
    
    A lot of this patch is taken from Mike Travis' "x86_64: Fold pda into
    per cpu area" patch.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    1a51e3a0
smp.c 10.9 KB