linux-kernel - Re: [patch V2 36/37] rseq: Switch to TIF

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Message-ID: <877byh2k13.ffs@tglx>
Date: Tue, 02 Sep 2025 13:03:52 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Sean Christopherson <seanjc@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Peter Zijlstra
 <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...nel.org>, Boqun
 Feng <boqun.feng@...il.com>, Paolo Bonzini <pbonzini@...hat.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 36/37] rseq: Switch to TIF_RSEQ if supported

On Mon, Aug 25 2025 at 13:02, Sean Christopherson wrote:
> On Sat, Aug 23, 2025, Thomas Gleixner wrote:
>> @@ -122,7 +122,7 @@ static inline void rseq_force_update(voi
>>   */
>>  static inline void rseq_virt_userspace_exit(void)
>>  {
>> -	if (current->rseq_event.sched_switch)
>> +	if (!IS_ENABLED(CONFIG_HAVE_GENERIC_TIF_BITS) && current->rseq_event.sched_switch)
>
> Rather than pivot on CONFIG_HAVE_GENERIC_TIF_BITS, which makes the "why" quite
> difficult to find/understand, what if this checks TIF_RSEQ == TIF_NOTIFY_RESUME?
> That would also allow architectures to define TIF_RSEQ without switching to the
> generic TIF bits implementation (though I don't know that we want to encourage
> that?).

Did you read the cover letter?

Consolidating on common infrastructure is the goal here. Stop
proliferating the architecture specific hackery, which has zero value
and justification. If people want to harvest the core improvements, then
they should get their act together and mop up their architecture
code. If they can't be bothered, so be it.

I'm happy to add a comment which explains that.

Thanks,

        tglx