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    Subject[PATCH 4.16 062/196] powerpc/64s: Fix dt_cpu_ftrs to have restore_cpu clear unwanted LPCR bits
    4.16-stable review patch.  If anyone has any objections, please let me know.


    From: Nicholas Piggin <>

    commit a57ac411832384eb93df4bfed2bf644c4089720e upstream.

    Presently the dt_cpu_ftrs restore_cpu will only add bits to the LPCR
    for secondaries, but some bits must be removed (e.g., UPRT for HPT).
    Not clearing these bits on secondaries causes checkstops when booting
    with disable_radix.

    restore_cpu can not just set LPCR, because it is also called by the
    idle wakeup code which relies on opal_slw_set_reg to restore the value
    of LPCR, at least on P8 which does not save LPCR to stack in the idle

    Fix this by including a mask of bits to clear from LPCR as well, which
    is used by restore_cpu.

    This is a little messy now, but it's a minimal fix that can be
    backported. Longer term, the idle SPR save/restore code can be
    reworked to completely avoid calls to restore_cpu, then restore_cpu
    would be able to unconditionally set LPCR to match boot processor

    Fixes: 5a61ef74f269f ("powerpc/64s: Support new device tree binding for discovering CPU features")
    Cc: # v4.12+
    Signed-off-by: Nicholas Piggin <>
    Signed-off-by: Michael Ellerman <>
    Signed-off-by: Greg Kroah-Hartman <>

    arch/powerpc/kernel/dt_cpu_ftrs.c | 12 +++++++++---
    1 file changed, 9 insertions(+), 3 deletions(-)

    --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
    +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
    @@ -84,6 +84,7 @@ static int hv_mode;

    static struct {
    u64 lpcr;
    + u64 lpcr_clear;
    u64 hfscr;
    u64 fscr;
    } system_registers;
    @@ -92,6 +93,8 @@ static void (*init_pmu_registers)(void);

    static void __restore_cpu_cpufeatures(void)
    + u64 lpcr;
    * LPCR is restored by the power on engine already. It can be changed
    * after early init e.g., by radix enable, and we have no unified API
    @@ -104,8 +107,10 @@ static void __restore_cpu_cpufeatures(vo
    * The best we can do to accommodate secondary boot and idle restore
    * for now is "or" LPCR with existing.
    - mtspr(SPRN_LPCR, system_registers.lpcr | mfspr(SPRN_LPCR));
    + lpcr = mfspr(SPRN_LPCR);
    + lpcr |= system_registers.lpcr;
    + lpcr &= ~system_registers.lpcr_clear;
    + mtspr(SPRN_LPCR, lpcr);
    if (hv_mode) {
    mtspr(SPRN_LPID, 0);
    mtspr(SPRN_HFSCR, system_registers.hfscr);
    @@ -325,8 +330,9 @@ static int __init feat_enable_mmu_hash_v
    u64 lpcr;

    + system_registers.lpcr_clear |= (LPCR_ISL | LPCR_UPRT | LPCR_HR);
    lpcr = mfspr(SPRN_LPCR);
    - lpcr &= ~LPCR_ISL;
    + lpcr &= ~(LPCR_ISL | LPCR_UPRT | LPCR_HR);
    mtspr(SPRN_LPCR, lpcr);

    cur_cpu_spec->mmu_features |= MMU_FTRS_HASH_BASE;

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      Last update: 2018-04-22 18:06    [W:3.416 / U:0.008 seconds]
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