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AHgh+RokWie+r/61XUFxGOjzOjqjfbIh7dLN0K7spN0NJamPx03rOt1OVnGBElZKbOUkSM2tLZAlDeXri56wq4yqyA==@lists.linux.dev X-Gm-Message-State: AOJu0YzwmYQPl20VbzZvwy1QLGZ2C76NtjQCwW1QSc5rGhfNYmEGfn2M J/ogGk/N+qDOvPhHmo+8GWVxDBkfFyfnCbQSK3wh4sHJtK/QKIt5RIkVzr2gRJNBsl4oReIEk0v ADSyA6w== X-Received: from pfiu19.prod.google.com ([2002:a05:6a00:1253:b0:84e:5c66:796c]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:1311:b0:847:9c3a:b77f with SMTP id d2e1a72fcca58-84fb55806bamr5778881b3a.35.1786550844921; Wed, 12 Aug 2026 09:07:24 -0700 (PDT) Date: Wed, 12 Aug 2026 09:07:24 -0700 In-Reply-To: <824a27d101d5b2e2a8a53fb81f5e4ecf15140a1f.camel@infradead.org> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260811162423.GL544626@ziepe.ca> <20260811172627.GN544626@ziepe.ca> <20260811181915.GO544626@ziepe.ca> <27f2326dc66d6341174c0e510aa518a1297b66ae.camel@infradead.org> <824a27d101d5b2e2a8a53fb81f5e4ecf15140a1f.camel@infradead.org> Message-ID: Subject: Re: [PATCH] mm/mmu_notifier: Remove non_block_start/end() from notifier invocation From: Sean Christopherson To: David Woodhouse Cc: Fred Griffoul , Paolo Bonzini , Jason Gunthorpe , akpm@linux-foundation.org, david@kernel.org, mhocko@suse.com, rostedt@goodmis.org, bigeasy@linutronix.de, simona.vetter@ffwll.ch, jglisse@redhat.com, christian.koenig@amd.com, paulmck@kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, Aug 12, 2026, David Woodhouse wrote: > On Tue, 2026-08-11 at 15:58 -0700, Sean Christopherson wrote: > > On Tue, Aug 11, 2026, David Woodhouse wrote: > > > On Tue, 2026-08-11 at 22:21 +0200, Paolo Bonzini wrote: > > > >=20 > > > > for_each_present_cpu(cpu) > > > > =C2=A0=C2=A0=C2=A0 if (per_cpu(kvm_gpc_reader, cpu) =3D=3D gpc) > > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cpumask_set_cpu(cpu, gpc= _readers); > > > > __kvm_kick_many_cpus(cpus, wait); > > >=20 > > >=20 > > > I'm literally sitting here watching you reinvent what SRCU already do= es. > >=20 > > The problem, for me at least, is that SRCU does this and a _lot_ more. > >=20 > > > Which, again, is *fine* given the behaviour of *these* read-side sect= ions. > >=20 > > Well, yeah.=C2=A0 Why use a nailgun to put a nail into the wall to hang= a picture > > frame? (other than the indisputable fact that power tools are fun).=C2= =A0 >=20 > It's not a nailgun, it's a drill. And in this analogy, my observation > that it works absolutely fine for us with *these* SRCU read-side users > ... is equivalent to finding the torque setting that lets you put it > into screwdriver mode. Yeah, but my concern is that there are KVM users out there that will put th= e drill into hammer drill mode, likely unknowingly, and then complain that "w= e" put a hole in their wall. What I want is a strong guarantee that the user can't configure bad torque/= mode settings, even unintentionally.