[PATCH 2/3] lib: sbi: Enable Smrnmi extension handler

[Nicholas Piggin]

On Mon, Feb 02, 2026 at 03:26:33PM +0000, Radim Krcmar wrote:
> 2026-01-29T00:13:42-08:00, Nylon Chen <nylon.chen at sifive.com>:
> > Enable the Smrnmi extension by:
> > 1. Adding sbi_rnmi_vector_init() to allocate per-HART RNMI context and enable RNMI via MNSTATUS.NMIE
> > 2. Saving and restoring CSR_MNSCRATCH and CSR_MNSTATUS across non-retentive suspend/resume
> > 3. Calling sbi_rnmi_vector_init() from the cold and warm init paths
> >
> > Co-developed-by: Zong Li <zong.li at sifive.com>
> > Signed-off-by: Zong Li <zong.li at sifive.com>
> > Suggested-by: Nick Hu <nick.hu at sifive.com>
> > Suggested-by: Samuel Holland <samuel.holland at sifive.com>
> > Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
> > Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
> > ---
> > diff --git a/include/sbi/sbi_platform.h b/include/sbi/sbi_platform.h
> > @@ -149,6 +149,15 @@ struct sbi_platform_operations {
> >  			unsigned long log2len);
> >  	/** platform specific pmp disable on current HART */
> >  	void (*pmp_disable)(unsigned int n);
> > +	/**
> > +	 * Platform-specific helper to program the RNMI trap vector.
> > +	 *
> > +	 * The core will call this from sbi_rnmi_vector_init() with the
> > +	 * firmware RNMI handler entry address (rnmi_handler) and the
> > +	 * cold_boot flag. Platforms that support Smrnmi should implement
> > +	 * this; others can leave it NULL.
> > +	 */
> 
> If the hart supports Smrnmi, then it begins with nmstatus.NMIE=0, which
> means that any exception is going to enter a critical state.
> The platform must somehow support Smrnmi to be useful, and I think it
> would be better not to do it behind opensbi's back.
> 
> If the platform wants to handle Smrnmi itself, it can hide Smrnmi from
> opensbi, so I think the requirement here would be better as MUST.
> 
> > +	int (*set_rnmi_trap_vector)(uintptr_t handler_addr, bool cold_boot);
> > diff --git a/lib/sbi/sbi_init.c b/lib/sbi/sbi_init.c
> > @@ -273,6 +273,10 @@ static void __noreturn init_coldboot(struct sbi_scratch *scratch, u32 hartid)
> >  	if (rc)
> >  		sbi_hart_hang();
> >  
> > +	rc = sbi_rnmi_vector_init(scratch, true);
> 
> Are we sure that earlier opensbi code won't try to trigger a trap before
> this point?  OpenSBI would fail to boot if it did...

This appears to come right after sbi_hart_init() which does a bunch of
CSR detection using traps, so I'm not sure if it can work.

Evgeny (+cc) has been doing a lot of work to enable Smrnmi on Ascalon
and unfortunately we did not see there is this duplicate work happening
upstream. His changes also has a few other things such as RNMI exception
vector setting, permits a platform specific handler, and has an Ascalon
platform implementation.

So I asked him to post what he has. The intention is not to disregard
this series, but to just show what he has. Hopefully the best of both
can be used.

Thanks,
Nick