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    Subject[PATCH 4.19 045/361] x86/mm/pat: Disable preemption around __flush_tlb_all()
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

    commit f77084d96355f5fba8e2c1fb3a51a393b1570de7 upstream.

    The WARN_ON_ONCE(__read_cr3() != build_cr3()) in switch_mm_irqs_off()
    triggers every once in a while during a snapshotted system upgrade.

    The warning triggers since commit decab0888e6e ("x86/mm: Remove
    preempt_disable/enable() from __native_flush_tlb()"). The callchain is:

    get_page_from_freelist() -> post_alloc_hook() -> __kernel_map_pages()

    with CONFIG_DEBUG_PAGEALLOC enabled.

    Disable preemption during CR3 reset / __flush_tlb_all() and add a comment
    why preemption has to be disabled so it won't be removed accidentaly.

    Add another preemptible() check in __flush_tlb_all() to catch callers with
    enabled preemption when PGE is enabled, because PGE enabled does not
    trigger the warning in __native_flush_tlb(). Suggested by Andy Lutomirski.

    Fixes: decab0888e6e ("x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()")
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20181017103432.zgv46nlu3hc7k4rq@linutronix.de
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/tlbflush.h | 6 ++++++
    arch/x86/mm/pageattr.c | 6 +++++-
    2 files changed, 11 insertions(+), 1 deletion(-)

    --- a/arch/x86/include/asm/tlbflush.h
    +++ b/arch/x86/include/asm/tlbflush.h
    @@ -469,6 +469,12 @@ static inline void __native_flush_tlb_on
    */
    static inline void __flush_tlb_all(void)
    {
    + /*
    + * This is to catch users with enabled preemption and the PGE feature
    + * and don't trigger the warning in __native_flush_tlb().
    + */
    + VM_WARN_ON_ONCE(preemptible());
    +
    if (boot_cpu_has(X86_FEATURE_PGE)) {
    __flush_tlb_global();
    } else {
    --- a/arch/x86/mm/pageattr.c
    +++ b/arch/x86/mm/pageattr.c
    @@ -2086,9 +2086,13 @@ void __kernel_map_pages(struct page *pag

    /*
    * We should perform an IPI and flush all tlbs,
    - * but that can deadlock->flush only current cpu:
    + * but that can deadlock->flush only current cpu.
    + * Preemption needs to be disabled around __flush_tlb_all() due to
    + * CR3 reload in __native_flush_tlb().
    */
    + preempt_disable();
    __flush_tlb_all();
    + preempt_enable();

    arch_flush_lazy_mmu_mode();
    }

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