linux-kernel - Re: [External] Re: [PATCH v3 5/8] riscv: smp: use NMI for CPU stop

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Message-ID: <CAEEQ3wmAn=9w=fR=OMTMF17_tAcEnsdJWL_w8fw-3wA-Bfi6xw@mail.gmail.com>
Date: Thu, 4 Dec 2025 13:28:45 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>
Cc: conor@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, luxu.kernel@...edance.com, 
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	jassisinghbrar@...il.com, conor.dooley@...rochip.com, 
	valentina.fernandezalanis@...rochip.com, catalin.marinas@....com, 
	will@...nel.org, maz@...nel.org, timothy.hayes@....com, lpieralisi@...nel.org, 
	arnd@...db.de, kees@...nel.org, tglx@...utronix.de, viresh.kumar@...aro.org, 
	boqun.feng@...il.com, linux-arm-kernel@...ts.infradead.org, 
	cleger@...osinc.com, atishp@...osinc.com, ajones@...tanamicro.com, 
	linux-riscv <linux-riscv-bounces@...ts.infradead.org>
Subject: Re: [External] Re: [PATCH v3 5/8] riscv: smp: use NMI for CPU stop

Hi Radim,

On Thu, Dec 4, 2025 at 12:07 PM Radim Krčmář <rkrcmar@...tanamicro.com> wrote:
>
> 2025-11-27T20:53:02+08:00, Yunhui Cui <cuiyunhui@...edance.com>:
> > Use NMI instead of IPI for CPU stop if RISC-V SSE NMI is supported.
> >
> > Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> > ---
> > diff --git a/drivers/firmware/riscv/riscv_sse_nmi.c b/drivers/firmware/riscv/riscv_sse_nmi.c
> > @@ -58,6 +58,7 @@ static int local_nmi_handler(u32 evt, void *arg, struct pt_regs *regs)
> >       type = atomic_read(this_cpu_ptr(&local_nmi));
> >
> >       NMI_HANDLE(LOCAL_NMI_CRASH, cpu_crash_stop, cpu, regs);
> > +     NMI_HANDLE(LOCAL_NMI_STOP, cpu_stop);
>
> Please document the intended preemption design for all SSE events,
> because it will be a nightmare if we forget some assumptions in the
> coming years.  (That includes the relative priorities of RAS/PMU/...)

Actually, LOCAL_NMI_CRASH, LOCAL_NMI_STOP, LOCAL_NMI_BACKTRACE,
LOCAL_NMI_KGDB, ... are all implemented via the single SSE event
SBI_SSE_EVENT_LOCAL_SOFTWARE_INJECTED. Per the SSE design, no
preemption will occur among CRASH, STOP, BACKTRACE, and KGDB events.

>
> Thanks.

Thanks,
Yunhui