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[141.95.202.232]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3d95df59e50sm9504812f8f.23.2025.09.03.12.54.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Sep 2025 12:54:57 -0700 (PDT) From: Alexandre Ghiti Date: Wed, 03 Sep 2025 19:54:29 +0000 Subject: [PATCH RFC] riscv: Do not handle break traps from kernel as nmi 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: quoted-printable Message-Id: <20250903-dev-alex-break_nmi_v1-v1-1-4a3d81c29598@rivosinc.com> X-B4-Tracking: v=1; b=H4sIAPScuGgC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDI1MDSwNj3ZTUMt3EnNQK3aSi1MTs+LzczPgyQ11T82RTYyPDNONUCwMloN6 CotS0zAqwudFKQW7OSrG1tQDR4C8EbAAAAA== X-Change-ID: 20250903-dev-alex-break_nmi_v1-57c5321f3e80 To: Peter Zijlstra , Steven Rostedt , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Guo Ren , =?utf-8?q?Bj=C3=B6rn_T=C3=B6pel?= Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Alexandre Ghiti X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=1916; i=alexghiti@rivosinc.com; h=from:subject:message-id; bh=ep2ByU6Sp3PUGleU/SkPJKB1vnJZEKwUxxPzvfc2zHY=; b=owGbwMvMwCGWYr9pz6TW912Mp9WSGDJ2zOUQju2NeZLt/efBtlSDKNmvc3VLoqScb2v/XMt29 an+IY39HaUsDGIcDLJiiiwK5gldLfZn62f/ufQeZg4rE8gQBi5OAZhItxPD/zq+v5/fzr6bXrSu ZMPx6vftCVu/bNnvsdBf8ceyozc26KUx/M99/HGOKsOcDa2nZq0prmblyUi9l8nxo1j6aJNWYvK bZi4A X-Developer-Key: i=alexghiti@rivosinc.com; a=openpgp; fpr=DC049C97114ED82152FE79A783E4BA75438E93E3 kprobe has been broken on riscv for quite some time. There is an attempt [1] to fix that which actually works. This patch works because it enables ARCH_HAVE_NMI_SAFE_CMPXCHG and that makes the ring buffer allocation succeed when handling a kprobe because we handle *all* kprobes in nmi context. We do so because Peter advised us to treat all kernel traps as nmi [2]. But that does not seem right for kprobe handling, so instead, treat break traps from kernel as non-nmi. Link: https://lore.kernel.org/linux-riscv/20250711090443.1688404-1-pulehui@= huaweicloud.com/ [1] Link: https://lore.kernel.org/linux-riscv/20250422094419.GC14170@noisy.prog= ramming.kicks-ass.net/ [2] Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") Cc: stable@vger.kernel.org Signed-off-by: Alexandre Ghiti --- This is clearly an RFC and this is likely not the right way to go, it is just a way to trigger a discussion about if handling kprobes in an nmi=20 context is the right way or not. --- arch/riscv/kernel/traps.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 80230de167def3c33db5bc190347ec5f87dbb6e3..90f36bb9b12d4ba0db0f084f878= 99156e3c7dc6f 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -315,11 +315,11 @@ asmlinkage __visible __trap_section void do_trap_brea= k(struct pt_regs *regs) local_irq_disable(); irqentry_exit_to_user_mode(regs); } else { - irqentry_state_t state =3D irqentry_nmi_enter(regs); + irqentry_state_t state =3D irqentry_enter(regs); =20 handle_break(regs); =20 - irqentry_nmi_exit(regs, state); + irqentry_exit(regs, state); } } =20 --- base-commit: ae9a687664d965b13eeab276111b2f97dd02e090 change-id: 20250903-dev-alex-break_nmi_v1-57c5321f3e80 Best regards, --=20 Alexandre Ghiti