linux-kernel - Re: [External] Re: [PATCH v3 0/8] riscv: Add Zalasr ISA extension support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAPYmKFunbrughXdG9Fpum6bxHVu9jmjQdgLVSJ_JA9z+GDsZbA@mail.gmail.com>
Date: Fri, 19 Sep 2025 20:12:14 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: Andrea Parri <parri.andrea@...il.com>
Cc: corbet@....net, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	alex@...ti.fr, will@...nel.org, peterz@...radead.org, boqun.feng@...il.com, 
	mark.rutland@....com, ajones@...tanamicro.com, brs@...osinc.com, 
	anup@...infault.org, atish.patra@...ux.dev, pbonzini@...hat.com, 
	shuah@...nel.org, devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, apw@...onical.com, joe@...ches.com, 
	linux-doc@...r.kernel.org, kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3 0/8] riscv: Add Zalasr ISA extension support

On Fri, Sep 19, 2025 at 7:06 PM Andrea Parri <parri.andrea@...il.com> wrote:
>
> > > > (not a review, just looking at this diff stat) is changing the fastpath
> > > >
> > > >   read_unlock()
> > > >   read_lock()
> > > >
> > > > from something like
> > > >
> > > >   fence rw,w
> > > >   amodadd.w
> > > >   amoadd.w
> > > >   fence r,rw
> > > >
> > > > to
> > > >
> > > >   fence rw,rw
> > > >   amoadd.w
> > > >   amoadd.w
> > > >   fence rw,rw
> > > >
> > > > no matter Zalasr or !Zalasr.  Similarly for other atomic operations with
> > > > release or acquire semantics.  I guess the change was not intentional?
> > > > If it was intentional, it should be properly mentioned in the changelog.
> > >
> > > Sorry about that. It is intended. The atomic operation before
> > > __atomic_acquire_fence or operation after __atomic_release_fence can
> > > be just a single ld or sd instruction instead of amocas or amoswap. In
> > > such cases, when the store release operation becomes 'sd.rl', the
> > > __atomic_acquire_fence via 'fence r, rw' can not ensure FENCE.TSO
> > > anymore. Thus I replace it with 'fence rw, rw'.
>
> But you could apply similar changes you performed for xchg & cmpxchg: use
> .AQ and .RL for other atomic RMW operations as well, no?  AFAICS, that is
> what arm64 actually does in arch/arm64/include/asm/atomic_{ll_sc,lse}.h .

I see. I will study the implementation of ARM and refine my patch. Thanks a lot.

Best regards,
Xu Lu

>
>   Andrea
>
>
> > This is also the common implementation on other architectures who use
> > aq/rl instructions like ARM. And you certainly already knew it~