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From: Alexandre Ghiti <alex@ghiti.fr>
To: Peter Zijlstra <peterz@infradead.org>,
	Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: "Steven Rostedt" <rostedt@goodmis.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Guo Ren" <guoren@kernel.org>, "Björn Töpel" <bjorn@rivosinc.com>,
	"Palmer Dabbelt" <palmer@rivosinc.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH RFC] riscv: Do not handle break traps from kernel as nmi
Date: Thu, 4 Sep 2025 09:59:46 +0200	[thread overview]
Message-ID: <ca18ee32-db74-4ec7-a6e2-805ac7abdee6@ghiti.fr> (raw)
In-Reply-To: <20250903202803.GQ4067720@noisy.programming.kicks-ass.net>

Hi Peter,

On 9/3/25 22:28, Peter Zijlstra wrote:
> On Wed, Sep 03, 2025 at 07:54:29PM +0000, Alexandre Ghiti wrote:
>> 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.
> You can put a kprobe inside: local_irq_disable(), no? Inside any random
> spinlock region in fact. How is the probe then not NMI like?


Yes yes, in that case that will be NMI-like, sorry this patch is coarse 
grain. The ideal solution would be to re-enable the interrupts if they 
were enabled at the moment of the trap. In that case, would that make 
sense to you?

Thanks,

Alex


>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

      reply	other threads:[~2025-09-04  8:15 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-03 19:54 Alexandre Ghiti
2025-09-03 20:28 ` Peter Zijlstra
2025-09-04  7:59   ` Alexandre Ghiti [this message]

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