linux-kernel - Re: [patch V2 15/37] rseq: Record interrupt from user space

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Message-ID: <87ecsp0xjp.ffs@tglx>
Date: Tue, 02 Sep 2025 15:54:50 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, LKML
 <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Peter Zijlstra <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Boqun Feng
 <boqun.feng@...il.com>, Paolo Bonzini <pbonzini@...hat.com>, Sean
 Christopherson <seanjc@...gle.com>, Wei Liu <wei.liu@...nel.org>, Dexuan
 Cui <decui@...rosoft.com>, x86@...nel.org, Arnd Bergmann <arnd@...db.de>,
 Heiko Carstens <hca@...ux.ibm.com>, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Huacai
 Chen <chenhuacai@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [patch V2 15/37] rseq: Record interrupt from user space

On Mon, Aug 25 2025 at 14:29, Mathieu Desnoyers wrote:
> On 2025-08-23 12:39, Thomas Gleixner wrote:
>> code. If your architecture does not use it, bad luck.
>> 
>
> Should we eventually add a "depends on GENERIC_IRQ_ENTRY" to RSEQ then ?

I wish we could, but that'd break MIPS, POWER and ARM*...

>> @@ -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();
>
> As long as this also covers the following scenarios I'm ok with this:
>
> - trap/exception from an rseq critical section,

It does. Traps and exceptions go through that entry path.

> - NMI over an rseq critical section.

That's irrelevant as NMIs are not going through the regular exit to user
path and therefore can't reschedule. If they trigger something which
requires a reschedule they raise IRQ work, which then goes through the
regular irqentry/exit path. 

Thanks,

        tglx