linux-kernel - Re: [PATCH v7 08/14] KVM: Rename mmu_notifier

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Message-ID: <ZG6EJoXbduApRsgV@google.com>
Date:   Wed, 24 May 2023 14:39:50 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kautuk Consul <kconsul@...ux.vnet.ibm.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 08/14] KVM: Rename mmu_notifier_*

On Wed, May 24, 2023, Peter Zijlstra wrote:
> On Wed, May 24, 2023 at 01:16:03PM -0700, Sean Christopherson wrote:
> > Of course, the only accesses outside of mmu_lock are reads, so on x86 that
> > "atomic" access is just a READ_ONCE() load, but that's not the case for all
> > architectures.
> 
> This is true on *all* archs. atomic_set() and atomic_read() are no more
> and no less than WRITE_ONCE() / READ_ONCE().

Ah, I take it s390's handcoded assembly routines are just a paranoid equivalents
and not truly special?  "l" and "st" do sound quite generic...

  commit 7657e41a0bd16c9d8b3cefe8fd5d6ac3c25ae4bf
  Author: Heiko Carstens <hca@...ux.ibm.com>
  Date:   Thu Feb 17 13:13:58 2011 +0100

    [S390] atomic: use inline asm
    
    Use inline assemblies for atomic_read/set(). This way there shouldn't
    be any questions or subtle volatile semantics left.

static inline int __atomic_read(const atomic_t *v)
{
	int c;

	asm volatile(
		"	l	%0,%1\n"
		: "=d" (c) : "R" (v->counter));
	return c;
}

static inline void __atomic_set(atomic_t *v, int i)
{
	asm volatile(
		"	st	%1,%0\n"
		: "=R" (v->counter) : "d" (i));
}