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Sat, 26 Sep 2026 13:03:41 -0700 (PDT) From: =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= To: ast@kernel.org, daniel@iogearbox.net Cc: john.fastabend@gmail.com, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= Subject: [RFC PATCH bpf-next 1/1] bpf: Remove redundant second __reg_deduce_bounds() call in reg_bounds_sync() Date: Sat, 26 Sep 2026 23:02:32 +0300 Message-ID: <20260926200313.281893-2-omermetekaya0@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260926200313.281893-1-omermetekaya0@gmail.com> References: <20260926200313.281893-1-omermetekaya0@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit reg_bounds_sync() calls __reg_deduce_bounds() twice in a row. With the current cnum implementation, the second call is now redundant. __reg_deduce_bounds() first intersects r32 with the 32-bit values representable by r64, then intersects r64 with the values allowed by r32. After one call, cnum64_cnum32_intersect() guarantees that every value in r64 has its corresponding u32 value in r32. So, a second call cannot further restrict either view. The old tnum + min/max representation could require multiple passes: tightening one of the 32-bit or 64-bit views could allow the other to be tightened further. The double call ensured that the bounds reached a fixpoint. With cnum, the first call already reaches the fixpoint. Signed-off-by: Ömer Mete Kaya --- kernel/bpf/verifier.c | 1 - 1 file changed, 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8d8923ad5..1cd923363 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2180,7 +2180,6 @@ static void reg_bounds_sync(struct bpf_reg_state *reg) __update_reg_bounds(reg); /* We might have learned something about the sign bit. */ __reg_deduce_bounds(reg); - __reg_deduce_bounds(reg); /* We might have learned some bits from the bounds. */ __reg_bound_offset(reg); /* Intersecting with the old var_off might have improved our bounds -- 2.55.0