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Tue, 13 Oct 2026 00:53:19 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([195.174.135.130]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48de0ac37acsm3531102f8f.34.2026.10.13.00.53.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 00:53:16 -0700 (PDT) Message-ID: <8ba6ca530f6f35c04ce7147ad601eee6bca2d792.camel@redhat.com> Subject: Re: [PATCH v2 0/3] rv: per-edge dwell-time statistics for per-cpu monitors From: Gabriele Monaco To: Steven Rostedt , Tobias Schaffner Cc: Jonathan Corbet , Shuah Khan , Masami Hiramatsu , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, rpm@xenomai.org, jan.kiszka@siemens.com Date: Tue, 13 Oct 2026 09:53:14 +0200 In-Reply-To: <20261012152129.4c57786c@gandalf.local.home> References: <20260911123439.463052-1-tobias.schaffner@siemens.com> <4759c9b0dacdf1f9c0cf47158895860dbd0ec401.camel@redhat.com> <20261012152129.4c57786c@gandalf.local.home> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== User-Agent: Evolution 3.60.2 (3.60.2-2.fc44) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: mDAu1inNZCwV3YkN9AEgINfIyJtFyuIdt6F-iMMP2wM_1791878000 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2026-10-12 at 15:21 -0400, Steven Rostedt wrote: > This brings back memories of conversations I had with Daniel. When asked > about how this is being used in formal verification of safety critical > systems, he told me that only the RV verifier itself needed to be verifie= d > and to show what it is verifying can be verified via it. For example, > running Linux in autonomous vehicles handling critical systems the watchd= og > had to be verified that it could catch lockups. As the watchdog would > trigger fail-safe mode if something went wrong. RV would be monitoring th= e > watchdog and if RV detected something it would panic the machine, which > would immediately force the vehicle into fail-safe mode (stop lots of > features and only keep those that can stop the vehicle safely). Yeah I talked to the same people working on that project, eventually there = were more problems like verifying RV can't be affected by the code it's verifyin= g. This is still an open problem though. > Can using BPF as the RV verifier be formally verified? As verification fo= r > RV monitors did look at the binary. Is BPF optimized to machine language > before it enters the kernel? If not, can we formally verify the BPF > verifier created the correct binary? Maybe, I don't know. As far as I understand, verifying the BPF verifier would take an insane amo= unt of work, the go-to approach is manually validating only the code you know y= ou are running. Let's say up to a point where you can realistically say it beh= aves like you want it to. In short, having a verifier doesn't add much value here, at least until som= eone verifies that too. Then there are the levels of indirection, BPF C code gets compiled to BPF bytecode and that gets JIT compiled inside the kernel. Now it's machine cod= e. If people are normally not validating clang/gcc produce machine code consis= tent to the verified source code, this case should be equivalent, but I'm just speculating here. Gabriele