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    SubjectRe: Dealing with the NMI mess
    On Fri, 24 Jul 2015 08:48:57 -0700
    Andy Lutomirski <luto@amacapital.net> wrote:

    > So by the time we detect that we've hit a watchpoint, the instruction
    > that tripped it is done and we don't need RF. Furthermore, after
    > reading 17.3.1.1: I *think* that regs->flags withh have RF *clear* if
    > we hit a watchpoint. So this might be as simple as:
    >
    > if ((dr6 && (0xf * DR_TRAP0) && (regs->flags & (X86_EFLAGS_RF |
    > X86_EFLAGS_IF)) == X86_EFLAGS_RF && !user_mode(regs))

    Also, wouldn't !(regs->X86_EFLAGS_IF) && !user_mode(regs) be a bug?
    When do we allow coming from userspace with interrupts disabled?

    -- Steve

    > for (i = 0; i < 4; i++)
    > if (dr6 & (DR_TRAP0<<i)) {
    > /* hit a kernel breakpoint with IF clear */
    > dr7 &= ~(DR_GLOBAL_ENABLE << (i * DR_ENABLE_SHIFT));
    > }
    >
    > I'm not saying that your code is wrong, but I think this is simpler
    > and avoids poking at yet more per-cpu state from NMI context, which is
    > kind of nice.
    >
    > If you don't like the RF games above, it would also be straightforward
    > to parse dr0..dr3 for each DR_TRAP bit that's set and see if it's a
    > breakpoint.
    >
    > --Andy



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