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

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Message-ID: <05d439ae-8f25-4b23-bb0c-3a3ce04eebbe@efficios.com>
Date: Tue, 28 Oct 2025 11:26:11 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Michael Jeanson <mjeanson@...icios.com>, Jens Axboe <axboe@...nel.dk>,
 Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, x86@...nel.org, Sean Christopherson
 <seanjc@...gle.com>, Wei Liu <wei.liu@...nel.org>
Subject: Re: [patch V6 15/31] rseq: Record interrupt from user space

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.

So what happens if such a trap is triggered from userspace,
and then scheduling happens on top of this trap ? Is this
skipping rseq ip fixup and rseq fields updates ?

Thanks,

Mathieu

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