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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432aa6b3069sm53583895e9.14.2024.11.07.02.02.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Nov 2024 02:02:56 -0800 (PST) Message-ID: <185b1a15-7e94-466d-a870-d7a2cc3bb890@redhat.com> Date: Thu, 7 Nov 2024 11:02:55 +0100 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: eric.auger@redhat.com Subject: Re: [kvm-unit-tests PATCH v2 2/3] lib/on-cpus: Add barrier after func call To: Andrew Jones , kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, kvmarm@lists.linux.dev Cc: atishp@rivosinc.com, jamestiotio@gmail.com, alexandru.elisei@arm.com References: <20241031123948.320652-5-andrew.jones@linux.dev> <20241031123948.320652-7-andrew.jones@linux.dev> From: Eric Auger In-Reply-To: <20241031123948.320652-7-andrew.jones@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: mK4hqnlwKUf7dyoQyI99ZGeTO1pett1MWsuz8d3l0Rg_1730973778 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/31/24 13:39, Andrew Jones wrote: > It's reasonable for users of on_cpu() and on_cpumask() to assume > they can read data that 'func' has written when the call completes. > Ensure the caller doesn't observe a completion (target cpus are again > idle) without also being able to observe any writes which were made > by func(). Do so by adding barriers to implement the following > > target-cpu calling-cpu > ---------- ----------- > func() /* store something */ /* wait for target to be idle */ > smp_wmb(); smp_rmb(); > set_cpu_idle(smp_processor_id(), true); /* load what func() stored */ > > Signed-off-by: Andrew Jones Reviewed-by: Eric Auger Eric > --- > lib/on-cpus.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/lib/on-cpus.c b/lib/on-cpus.c > index f6072117fa1b..356f284be61b 100644 > --- a/lib/on-cpus.c > +++ b/lib/on-cpus.c > @@ -79,6 +79,7 @@ void do_idle(void) > smp_wait_for_event(); > smp_rmb(); > on_cpu_info[cpu].func(on_cpu_info[cpu].data); > + smp_wmb(); /* pairs with the smp_rmb() in on_cpu() and on_cpumask() */ > } > } > > @@ -145,12 +146,14 @@ void on_cpumask(const cpumask_t *mask, void (*func)(void *data), void *data) > smp_wait_for_event(); > for_each_cpu(cpu, mask) > cpumask_clear_cpu(me, &on_cpu_info[cpu].waiters); > + smp_rmb(); /* pairs with the smp_wmb() in do_idle() */ > } > > void on_cpu(int cpu, void (*func)(void *data), void *data) > { > on_cpu_async(cpu, func, data); > cpu_wait(cpu); > + smp_rmb(); /* pairs with the smp_wmb() in do_idle() */ > } > > void on_cpus(void (*func)(void *data), void *data)