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    Subject[PATCH 5.2 157/313] x86/mm/pti: Do not invoke PTI functions when PTI is disabled
    Date
    From: Thomas Gleixner <tglx@linutronix.de>

    [ Upstream commit 990784b57731192b7d90c8d4049e6318d81e887d ]

    When PTI is disabled at boot time either because the CPU is not affected or
    PTI has been disabled on the command line, the boot code still calls into
    pti_finalize() which then unconditionally invokes:

    pti_clone_entry_text()
    pti_clone_kernel_text()

    pti_clone_kernel_text() was called unconditionally before the 32bit support
    was added and 32bit added the call to pti_clone_entry_text().

    The call has no side effects as cloning the page tables into the available
    second one, which was allocated for PTI does not create damage. But it does
    not make sense either and in case that this functionality would be extended
    later this might actually lead to hard to diagnose issues.

    Neither function should be called when PTI is runtime disabled. Make the
    invocation conditional.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
    Acked-by: Ingo Molnar <mingo@kernel.org>
    Acked-by: Song Liu <songliubraving@fb.com>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20190828143124.063353972@linutronix.de
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/mm/pti.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
    index b196524759ec5..ba22b50f4eca2 100644
    --- a/arch/x86/mm/pti.c
    +++ b/arch/x86/mm/pti.c
    @@ -666,6 +666,8 @@ void __init pti_init(void)
    */
    void pti_finalize(void)
    {
    + if (!boot_cpu_has(X86_FEATURE_PTI))
    + return;
    /*
    * We need to clone everything (again) that maps parts of the
    * kernel image.
    --
    2.20.1


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