On Thu, Oct 24, 2019 at 10:52:59PM +0200, Thomas Gleixner wrote: > is just undefined behaviour and I personally consider it to be a plain bug. I concur. > Just for the record: This results in running a resulting or even completely > unrelated signal handler with interrupts disabled as well. > > Whatever we decide it is, leaving it completely inconsistent is not a > solution at all. The options are: > > 1) Always do conditional tracing depending on the user_regs->eflags.IF > state. > > 2) #1 + warn once when syscalls and exceptions (except NMI/MCE) happen > and user_regs->eflags.IF is cleared. > > 3a) #2 + enforce signal handling to run with interrupts enabled. > > 3b) #2 + set regs->eflags.IF. So the state is always correct from the > kernel POV. Of course that changes existing behaviour, but its > changing undefined and inconsistent behaviour. > > 4) Let iopl(level) return -EPERM if level == 3. > > Yeah, I know it's not possible due to regressions (DPKD uses iopl(3)), > but TBH that'd be the sanest option of all. > > Of course the infinite wisdom of hardware designers tied IN, INS, OUT, > OUTS and CLI/STI together on IOPL so we cannot even distangle them in > any way. > > The only way out would be to actually use a full 8K sized I/O bitmap, > but that's a massive pain as it has to be copied on every context > switch. > > Really pretty options to chose from ... If 4 is out (and I'm afraid it might be), then I'm on record for liking 3b.
