[PATCH v4] powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

[Mahesh J Salgaonkar]

On 2024-03-07 22:43:07 Thu, Michael Ellerman wrote:
> > diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> > index a4196ab1d0167..0b96464ff0339 100644
> > --- a/arch/powerpc/include/asm/interrupt.h
> > +++ b/arch/powerpc/include/asm/interrupt.h
> > @@ -336,6 +336,14 @@ static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, struct inte
> >  	if (IS_ENABLED(CONFIG_KASAN))
> >  		return;
> >  
> > +	/*
> > +	 * Likewise, do not use it in real mode if percpu first chunk is not
> > +	 * embedded. With CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there
> > +	 * are chances where percpu allocation can come from vmalloc area.
> > +	 */
> > +	if (IS_ENABLED(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && !is_embed_first_chunk)
> 
> I think this would be clearer if it was inverted, eg:
> 
>         if (percpu_first_chunk_is_paged)
>                return;

Agree.

> 
> That way you shouldn't need to check CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK here.
> Instead it can be part of the ifdef in the header.
> 
> > @@ -351,6 +359,8 @@ static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct inter
> >  		// no nmi_exit for a pseries hash guest taking a real mode exception
> >  	} else if (IS_ENABLED(CONFIG_KASAN)) {
> >  		// no nmi_exit for KASAN in real mode
> > +	} else if (IS_ENABLED(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && !is_embed_first_chunk) {
> > +		// no nmi_exit if percpu first chunk is not embedded
> >  	} else {
> >  		nmi_exit();
> >  	}
> > diff --git a/arch/powerpc/include/asm/percpu.h b/arch/powerpc/include/asm/percpu.h
> > index 8e5b7d0b851c6..e24063eb0b33b 100644
> > --- a/arch/powerpc/include/asm/percpu.h
> > +++ b/arch/powerpc/include/asm/percpu.h
> > @@ -15,6 +15,16 @@
> >  #endif /* CONFIG_SMP */
> >  #endif /* __powerpc64__ */
> >  
> > +#ifdef CONFIG_PPC64
> > +#include <linux/jump_label.h>
> > +DECLARE_STATIC_KEY_FALSE(__percpu_embed_first_chunk);
> > +
> > +#define is_embed_first_chunk	\
> > +		(static_key_enabled(&__percpu_embed_first_chunk.key))
> > +#else
> > +#define is_embed_first_chunk	true
> > +#endif /* CONFIG_PPC64 */
> > +
> 
> Something like:
> 
> #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> #include <linux/jump_label.h>
> DECLARE_STATIC_KEY_FALSE(__percpu_first_chunk_is_paged);
> 
> #define percpu_first_chunk_is_paged	\
> 		(static_key_enabled(&__percpu_first_chunk_is_paged.key))
> #else
> #define percpu_first_chunk_is_paged	false
> #endif /* CONFIG_PPC64 */

Sure, will fix it.

> 
> > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> > index 2f19d5e944852..e04f0ff69d4b6 100644
> > --- a/arch/powerpc/kernel/setup_64.c
> > +++ b/arch/powerpc/kernel/setup_64.c
> > @@ -834,6 +834,7 @@ static __init int pcpu_cpu_to_node(int cpu)
> >  
> >  unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
> >  EXPORT_SYMBOL(__per_cpu_offset);
> > +DEFINE_STATIC_KEY_FALSE(__percpu_embed_first_chunk);
> >  
> >  void __init setup_per_cpu_areas(void)
> >  {
> > @@ -869,6 +870,8 @@ void __init setup_per_cpu_areas(void)
> >  			pr_warn("PERCPU: %s allocator failed (%d), "
> >  				"falling back to page size\n",
> >  				pcpu_fc_names[pcpu_chosen_fc], rc);
> > +		else
> > +			static_key_enable(&__percpu_embed_first_chunk.key);
> >  	}
> >  
> >  	if (rc < 0)
>  
> Finally, the current patch breaks the microwatt build:
> 
>   $ make microwatt_defconfig ; make -s -j (nproc)
>   make[1]: Entering directory '/home/michael/linux/.build'
>     GEN     Makefile
>   #
>   # configuration written to .config
>   #
>   make[1]: Leaving directory '/home/michael/linux/.build'
>   ld: arch/powerpc/kernel/traps.o:(.toc+0x0): undefined reference to `__percpu_embed_first_chunk'
>   ld: arch/powerpc/kernel/mce.o:(.toc+0x0): undefined reference to `__percpu_embed_first_chunk'
>   make[3]: *** [../scripts/Makefile.vmlinux:37: vmlinux] Error 1
> 
> I guess because it has CONFIG_JUMP_LABEL=n?

Even with CONFIG_JUMP_LABEL=n it should still work. Let me take look and
fix this for microwatt build.

Thanks for your review.
-Mahesh.

> 
> cheers

-- 
Mahesh J Salgaonkar