Re: [patch V6 15/31] rseq: Record interrupt from user space

[Mathieu Desnoyers]

On 2025-10-28 13:02, Thomas Gleixner wrote:
> On Tue, Oct 28 2025 at 11:26, Mathieu Desnoyers wrote:
> > On 2025-10-27 04:44, Thomas Gleixner wrote:
> > [...]
> > > @@ -281,6 +281,7 @@ static __always_inline void exit_to_user
> > >    static __always_inline void irqentry_enter_from_user_mode(struct pt_regs *regs)
> > >    {
> > >    	enter_from_user_mode(regs);
> > > +	rseq_note_user_irq_entry();
> > >    }
> > >    
> > Looking at x86, both exc_debug_user() and exc_int3() invoke
> > irqentry_enter_from_user_mode(), but there are various
> > other traps that can come from userspace (e.g. math_error,
> > exc_general_protection, ...). Some of those traps don't
> > necessarily end with a signal delivery to the offending
> > process. And some of those traps enable interrupts.
>
> They all go through irqentry_enter_from_user_mode(). See
> DEFINE_IDTENTRY*() macros. They invoke:
>
>     irqentry_enter()
>       if (user_mode())
>          irqentry_enter_from_user_mode();
>
> If that wouldn't be the case then all the RCU/NOHZ magic would not work
> either. So any exception, trap, interrupt must go through this to
> establish state correctly. Whether that's explicit as it's required for
> int3 and debug_user or implicit through the IDTENTRY magic.

That's what I missed, thanks for the explanation.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com