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    Subject[PATCH 5.15 215/277] highmem: fix checks in __kmap_local_sched_{in,out}
    Date
    From: Max Filippov <jcmvbkbc@gmail.com>

    commit 66f133ceab7456c789f70a242991ed1b27ba1c3d upstream.

    When CONFIG_DEBUG_KMAP_LOCAL is enabled __kmap_local_sched_{in,out} check
    that even slots in the tsk->kmap_ctrl.pteval are unmapped. The slots are
    initialized with 0 value, but the check is done with pte_none. 0 pte
    however does not necessarily mean that pte_none will return true. e.g.
    on xtensa it returns false, resulting in the following runtime warnings:

    WARNING: CPU: 0 PID: 101 at mm/highmem.c:627 __kmap_local_sched_out+0x51/0x108
    CPU: 0 PID: 101 Comm: touch Not tainted 5.17.0-rc7-00010-gd3a1cdde80d2-dirty #13
    Call Trace:
    dump_stack+0xc/0x40
    __warn+0x8f/0x174
    warn_slowpath_fmt+0x48/0xac
    __kmap_local_sched_out+0x51/0x108
    __schedule+0x71a/0x9c4
    preempt_schedule_irq+0xa0/0xe0
    common_exception_return+0x5c/0x93
    do_wp_page+0x30e/0x330
    handle_mm_fault+0xa70/0xc3c
    do_page_fault+0x1d8/0x3c4
    common_exception+0x7f/0x7f

    WARNING: CPU: 0 PID: 101 at mm/highmem.c:664 __kmap_local_sched_in+0x50/0xe0
    CPU: 0 PID: 101 Comm: touch Tainted: G W 5.17.0-rc7-00010-gd3a1cdde80d2-dirty #13
    Call Trace:
    dump_stack+0xc/0x40
    __warn+0x8f/0x174
    warn_slowpath_fmt+0x48/0xac
    __kmap_local_sched_in+0x50/0xe0
    finish_task_switch$isra$0+0x1ce/0x2f8
    __schedule+0x86e/0x9c4
    preempt_schedule_irq+0xa0/0xe0
    common_exception_return+0x5c/0x93
    do_wp_page+0x30e/0x330
    handle_mm_fault+0xa70/0xc3c
    do_page_fault+0x1d8/0x3c4
    common_exception+0x7f/0x7f

    Fix it by replacing !pte_none(pteval) with pte_val(pteval) != 0.

    Link: https://lkml.kernel.org/r/20220403235159.3498065-1-jcmvbkbc@gmail.com
    Fixes: 5fbda3ecd14a ("sched: highmem: Store local kmaps in task struct")
    Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/highmem.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/mm/highmem.c
    +++ b/mm/highmem.c
    @@ -627,7 +627,7 @@ void __kmap_local_sched_out(void)

    /* With debug all even slots are unmapped and act as guard */
    if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
    - WARN_ON_ONCE(!pte_none(pteval));
    + WARN_ON_ONCE(pte_val(pteval) != 0);
    continue;
    }
    if (WARN_ON_ONCE(pte_none(pteval)))
    @@ -664,7 +664,7 @@ void __kmap_local_sched_in(void)

    /* With debug all even slots are unmapped and act as guard */
    if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
    - WARN_ON_ONCE(!pte_none(pteval));
    + WARN_ON_ONCE(pte_val(pteval) != 0);
    continue;
    }
    if (WARN_ON_ONCE(pte_none(pteval)))

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