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    Subject[PATCH 4.4 024/312] MIPS: Fix 64-bit HTW configuration
    Date
    From: James Hogan <james.hogan@imgtec.com>

    commit aa76042a016474775ccd187c068669148c30c3bb upstream.

    The Hardware page Table Walker (HTW) is being misconfigured on 64-bit
    kernels. The PWSize.PS (pointer size) bit determines whether pointers
    within directories are loaded as 32-bit or 64-bit addresses, but was
    never being set to 1 for 64-bit kernels where the unsigned long in pgd_t
    is 64-bits wide.

    This actually reduces rather than improves performance when the HTW is
    enabled on P6600 since the HTW is initiated lots, but walks are all
    aborted due I think to bad intermediate pointers.

    Since we were already taking the width of the PTEs into account by
    setting PWSize.PTEW, which is the left shift applied to the page table
    index *in addition to* the native pointer size, we also need to reduce
    PTEW by 1 when PS=1. This is done by calculating PTEW based on the
    relative size of pte_t compared to pgd_t.

    Finally in order for the HTW to be used when PS=1, the appropriate
    XK/XS/XU bits corresponding to the different 64-bit segments need to be
    set in PWCtl. We enable only XU for now to enable walking for XUSeg.

    Supporting walking for XKSeg would be a bit more involved so is left for
    a future patch. It would either require the use of a per-CPU top level
    base directory if supported by the HTW (a bit like pgd_current but with
    a second entry pointing at swapper_pg_dir), or the HTW would prepend bit
    63 of the address to the global directory index which doesn't really
    match how we split user and kernel page directories.

    Fixes: cab25bc7537b ("MIPS: Extend hardware table walking support to MIPS64")
    Signed-off-by: James Hogan <james.hogan@imgtec.com>
    Cc: Paul Burton <paul.burton@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Patchwork: https://patchwork.linux-mips.org/patch/13364/
    Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/mips/mm/tlbex.c | 14 ++++++++++++--
    1 file changed, 12 insertions(+), 2 deletions(-)

    --- a/arch/mips/mm/tlbex.c
    +++ b/arch/mips/mm/tlbex.c
    @@ -2329,15 +2329,25 @@ static void config_htw_params(void)
    if (CONFIG_PGTABLE_LEVELS >= 3)
    pwsize |= ilog2(PTRS_PER_PMD) << MIPS_PWSIZE_MDW_SHIFT;

    - pwsize |= ilog2(sizeof(pte_t)/4) << MIPS_PWSIZE_PTEW_SHIFT;
    + /* Set pointer size to size of directory pointers */
    + if (config_enabled(CONFIG_64BIT))
    + pwsize |= MIPS_PWSIZE_PS_MASK;
    + /* PTEs may be multiple pointers long (e.g. with XPA) */
    + pwsize |= ((PTE_T_LOG2 - PGD_T_LOG2) << MIPS_PWSIZE_PTEW_SHIFT)
    + & MIPS_PWSIZE_PTEW_MASK;

    write_c0_pwsize(pwsize);

    /* Make sure everything is set before we enable the HTW */
    back_to_back_c0_hazard();

    - /* Enable HTW and disable the rest of the pwctl fields */
    + /*
    + * Enable HTW (and only for XUSeg on 64-bit), and disable the rest of
    + * the pwctl fields.
    + */
    config = 1 << MIPS_PWCTL_PWEN_SHIFT;
    + if (config_enabled(CONFIG_64BIT))
    + config |= MIPS_PWCTL_XU_MASK;
    write_c0_pwctl(config);
    pr_info("Hardware Page Table Walker enabled\n");


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