linux-kernel - Re: [patch V2 23/37] rseq: Provide and use rseq_set

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Message-ID: <87qzwozudw.ffs@tglx>
Date: Tue, 02 Sep 2025 18:33:47 +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 23/37] rseq: Provide and use rseq_set_uids()

On Tue, Sep 02 2025 at 16:08, Thomas Gleixner wrote:
> On Tue, Aug 26 2025 at 10:52, Mathieu Desnoyers wrote:
>>> +
>>> +	/* Cache the new values */
>>> +	t->rseq_ids.cpu_cid = ids->cpu_cid;
>>
>> I may be missing something, but I think we're missing updates to
>> t->rseq_ids.mm_cid and we may want to keep track of t->rseq_ids.node_id
>> as well.
>
> Oops. I'm sure I had that mm_cid caching, but somehow dropped it. And
> again, no need to keep track of the node id. It's stable vs. CPU ID.

Correcting myself. You are missing that this caches the compound value
and not only the CPU id.