> On Jun 12, 2020, at 2:01 AM, Thomas Gleixner <[email protected]> wrote:
>
> Andy Lutomirski <[email protected]> writes:
>> On Thu, Jun 11, 2020 at 4:22 PM Andy Lutomirski <[email protected]> wrote:
>>
>> Two bugs here.
>>
>> 1. We had an issue with WARN. Patch sent.
>
> Grabbed it
>
>> 2. idtentry.h has, for x86_32:
>>
>> # define DEFINE_IDTENTRY_IST DEFINE_IDTENTRY
>>
>> This is nonsense. It's getting late over here and I'd rather focus on
>> the more interesting RCU issue, so that's all from me today.
>
> Well, this might be nonsense, but it's exactly matching the current code
> in mainline which, e.g. for #DB does:
>
> SYM_CODE_START(debug)
> /*
> * Entry from sysenter is now handled in common_exception
> */
> ASM_CLAC
> pushl $0
> pushl $do_debug
> jmp common_exception
> SYM_CODE_END(debug)
>
> There is no IST on 32bit, never was. We do software stack switching for
> device interrupts, but that's a different story.
>
DEFINE_IDTENTRY does the idtentry_enter_cond_rcu() dance, which isn’t intended
to be safe from NMI context. It should probably map to DEFINE_IDTENTRY_RAW()
instead. The specific issue is that NMI ends up there, and at least
DEFINE_IDTENTRY_NMI should be raw.
I haven’t tried this at all, nor have I dug through all the users of these
macros to check what they expect. Perhaps we should not have the _IST one
defined at all on 32 bit and rename it to DEFINE_IDTENTRY_IST_RAW on 64 bit to
make it more clear what’s going on when reading the C code.
Or maybe I’m too sleepy and I’m nuts. But I don’t think I am.
> Thanks,
>
> tglx
