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    Subject[PATCH 31/43] x86/mm/kaiser: Map entry stack variable
    Date
    From: Dave Hansen <dave.hansen@linux.intel.com>

    There are times where the kernel is entered but there is no
    safe stack, like at SYSCALL entry. To obtain a safe stack, we
    have to clobber %rsp and store the clobbered value in
    'rsp_scratch'.

    Map this to userspace to allow us to do this stack switch before
    the CR3 switch.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: daniel.gruss@iaik.tugraz.at
    Cc: hughd@google.com
    Cc: keescook@google.com
    Cc: linux-mm@kvack.org
    Cc: luto@kernel.org
    Cc: michael.schwarz@iaik.tugraz.at
    Cc: moritz.lipp@iaik.tugraz.at
    Cc: richard.fellner@student.tugraz.at
    Link: https://lkml.kernel.org/r/20171123003459.C0FF167A@viggo.jf.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/kernel/process_64.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    index bafe65b08697..9a0220aa2bf9 100644
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -59,7 +59,7 @@
    #include <asm/unistd_32_ia32.h>
    #endif

    -__visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
    +__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch);

    /* Prints also some state that isn't saved in the pt_regs */
    void __show_regs(struct pt_regs *regs, int all)
    --
    2.14.1
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