linux-kernel - Re: [External] Re: [PATCH 3/3] riscv: crash: use NMI to stop the CPU

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Message-ID: <CAEEQ3wk8w1q8Ujpq+6fyRPP+zqTy6_q22K-g681VZyVXstPaDg@mail.gmail.com>
Date: Mon, 3 Nov 2025 22:10:25 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>
Cc: Conor Dooley <conor@...nel.org>, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, luxu.kernel@...edance.com, 
	atishp@...osinc.com, cleger@...osinc.com, ajones@...tanamicro.com, 
	apatel@...tanamicro.com, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, songshuaishuai@...ylab.org, 
	bjorn@...osinc.com, charlie@...osinc.com, masahiroy@...nel.org, 
	valentina.fernandezalanis@...rochip.com, jassisinghbrar@...il.com, 
	conor.dooley@...rochip.com, 
	linux-riscv <linux-riscv-bounces@...ts.infradead.org>
Subject: Re: [External] Re: [PATCH 3/3] riscv: crash: use NMI to stop the CPU

Hi Radim,

On Tue, Oct 28, 2025 at 8:36 PM Radim Krčmář <rkrcmar@...tanamicro.com> wrote:
>
> 2025-10-28T10:42:12+00:00, Conor Dooley <conor@...nel.org>:
> > On Mon, Oct 27, 2025 at 09:34:31PM +0800, Yunhui Cui wrote:
> >> NMI is more robust than IPI for stopping CPUs during crashes,
> >> especially with interrupts disabled. Add SBI_SSE_EVENT_LOCAL_CRASH_NMI
> >> eventid to implement NMI for stopping CPUs.
> >>
> >> Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> >> ---
> >> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> >> @@ -487,6 +487,7 @@ enum sbi_sse_attr_id {
> >>  #define SBI_SSE_EVENT_GLOBAL_LOW_PRIO_RAS   0x00108000
> >>  #define SBI_SSE_EVENT_LOCAL_SOFTWARE_INJECTED       0xffff0000
> >>  #define SBI_SSE_EVENT_LOCAL_UNKNOWN_NMI             0xffff0001
> >> +#define SBI_SSE_EVENT_LOCAL_CRASH_NMI               0xffff0002
>
> This event isn't defined in the SBI pull request.
>
> I assume it's a pure software event that the platform shouldn't inject.
> If we want to reserve more events for software use, why not make them
> generic, like SBI_SSE_EVENT_LOCAL_SOFTWARE_INJECTED?

In fact, it's not just crash NMI, but also stop NMI, kgdb NMI, etc. An
event can only register one SSE handler. If all use
SBI_SSE_EVENT_LOCAL_SOFTWARE_INJECTED, we'll have to execute each
different NMI handler in sequence within the SSE handler, with each
NMI handler checking for itself if there are NMIs of its type to
process.
Is that what you mean too?

>
> Thanks.

Thanks,
Yunhui