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    SubjectRe: [PATCH] enable interrupts in user path of page fault.


    On Thu, 7 Jun 2007, Andrew Morton wrote:
    >
    > Interrupts got disabled here because do_page_fault() is an
    > interrupt-disabling trap, yes?

    Yes - and it has to be: we want to disable preemption and interrupts that
    can fault on the vmalloc space, until we've at least saved away %cr2. We
    had bugs in that area before.

    > The patch looks reasonable to me: a slight reduction in interrupt-off
    > latency when really weird things are happening.

    I applied it as obviously correct.

    > The patch also breaks things, I think: if userspace is running with
    > interrupts disabled and tries to access kernel memory it will presently
    > whizz through the kernel without ever enabling interrupts. With this
    > change, the kernel will now enable interrupts, which is presumably not what
    > the application wanted.

    Well, we *do* enable interrupts for real page faults anyway, and this
    whole code just triggers for the case where we'd send a SIGSEGV. If some
    silly app really thought it could do that with interrupts disabled, it was
    wrong before too (we'd hit a reschedule point and enable them there
    anyway).

    Linus
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