• Matt Redfearn's avatar
    MIPS: Only change $28 to thread_info if coming from user mode · 510d8636
    Matt Redfearn authored
    The SAVE_SOME macro is used to save the execution context on all
    exceptions.
    If an exception occurs while executing user code, the stack is switched
    to the kernel's stack for the current task, and register $28 is switched
    to point to the current_thread_info, which is at the bottom of the stack
    region.
    If the exception occurs while executing kernel code, the stack is left,
    and this change ensures that register $28 is not updated. This is the
    correct behaviour when the kernel can be executing on the separate irq
    stack, because the thread_info will not be at the base of it.
    
    With this change, register $28 is only switched to it's kernel
    conventional usage of the currrent thread info pointer at the point at
    which execution enters kernel space. Doing it on every exception was
    redundant, but OK without an IRQ stack, but will be erroneous once that
    is introduced.
    Signed-off-by: default avatarMatt Redfearn <matt.redfearn@imgtec.com>
    Acked-by: default avatarJason A. Donenfeld <jason@zx2c4.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: James Hogan <james.hogan@imgtec.com>
    Cc: Paul Burton <paul.burton@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Cc: linux-kernel@vger.kernel.org
    Patchwork: https://patchwork.linux-mips.org/patch/14742/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    510d8636
stackframe.h 9.33 KB