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    SubjectRe: [PATCH v2 6/8] x86/entry: add unwind hint annotations
    On Thu, Jun 29, 2017 at 10:05 PM, Andy Lutomirski <luto@kernel.org> wrote:
    > Hmm. There's another option that might be considerably nicer, though:
    > put the IRQ stack at a known (at link time) position *in percpu
    > space*. (Presumably it already is -- I haven't checked.) Then we do:
    >
    > .macro ENTER_IRQ_STACK old_rsp
    > DEBUG_ENTRY_ASSERT_IRQS_OFF
    > movq %rsp, \old_rsp
    > incl PER_CPU_VAR(irq_count)
    >
    > /*
    > * Right now, if we just incremented irq_count to zero, we've
    > * claimed the IRQ stack but we haven't switched to it yet.
    > * Anything that can interrupt us here without using IST
    > * must be *extremely* careful to limit its stack usage.
    > */
    > jnz .Lpush_old_rsp_\@
    > movq \old_rsp, PER_CPU_VAR(top_word_in_irq_stack)
    > movq PER_CPU_VAR(irq_stack_ptr), %rsp
    > .Lpush_old_rsp_\@:
    > pushq \old_rsp
    > .endm
    >

    How about the two commits here (well, soon to be there once gitweb catches up):

    https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_irq_stack&id=0f56a55bb133cd53ccb78ca51378086296618322

    If you like them, want to add them to your series?

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