linux-kernel - Re: [patch V4 27/36] rseq: Implement fast path for exit to user

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Message-ID: <87y0qlq8eb.ffs@tglx>
Date: Thu, 11 Sep 2025 18:08:28 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 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>, 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 V4 27/36] rseq: Implement fast path for exit to user

On Thu, Sep 11 2025 at 10:27, Mathieu Desnoyers wrote:
> On 2025-09-08 17:32, Thomas Gleixner wrote:
>> The initial decision to invoke any of this is based on two flags in the
>> event struct: @has_rseq and @sched_switch. The decision is in pseudo ASM:
>> 
>>        load	tsk::event::has_rseq
>>        and	tsk::event::sched_switch
>
> I suspect that my earlier comment about has_rseq and AND applies here
> as well. We could probably remove the has_rseq load and the AND
> altogether and just load sched_switch for the conditional branch ?

Same comment as before.