[PATCH v2] powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

[Mahesh J Salgaonkar]

On 2024-02-12 08:06:25 Mon, Christophe Leroy wrote:
> 
> 
> Le 05/02/2024 à 06:36, Mahesh Salgaonkar a écrit :
> > [Vous ne recevez pas souvent de courriers de mahesh at linux.ibm.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > nmi_enter()/nmi_exit() touches per cpu variables which can lead to kernel
> > crash when invoked during real mode interrupt handling (e.g. early HMI/MCE
> > interrupt handler) if percpu allocation comes from vmalloc area.
> > 
> > Early HMI/MCE handlers are called through DEFINE_INTERRUPT_HANDLER_NMI()
> > wrapper which invokes nmi_enter/nmi_exit calls. We don't see any issue when
> > percpu allocation is from the embedded first chunk. However with
> > CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there are chances where percpu
> > allocation can come from the vmalloc area.
> > 
> > With kernel command line "percpu_alloc=page" we can force percpu allocation
> > to come from vmalloc area and can see kernel crash in machine_check_early:
> > 
> > [    1.215714] NIP [c000000000e49eb4] rcu_nmi_enter+0x24/0x110
> > [    1.215717] LR [c0000000000461a0] machine_check_early+0xf0/0x2c0
> > [    1.215719] --- interrupt: 200
> > [    1.215720] [c000000fffd73180] [0000000000000000] 0x0 (unreliable)
> > [    1.215722] [c000000fffd731b0] [0000000000000000] 0x0
> > [    1.215724] [c000000fffd73210] [c000000000008364] machine_check_early_common+0x134/0x1f8
> > 
> > Fix this by avoiding use of nmi_enter()/nmi_exit() in real mode if percpu
> > first chunk is not embedded.
> > 
> > Signed-off-by: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> > ---
> > Changes in v2:
> > - Rebase to upstream master
> > - Use jump_labels, if CONFIG_JUMP_LABEL is enabled, to avoid redoing the
> >    test at each interrupt entry.
> > - v1 is at https://lore.kernel.org/linuxppc-dev/164578465828.74956.6065296024817333750.stgit@jupiter/
> > ---
> >   arch/powerpc/include/asm/interrupt.h | 14 ++++++++++++++
> >   arch/powerpc/include/asm/percpu.h    | 11 +++++++++++
> >   arch/powerpc/kernel/setup_64.c       | 12 ++++++++++++
> >   3 files changed, 37 insertions(+)
> > 
> > diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> > index a4196ab1d0167..3b4e17c23d9a9 100644
> > --- a/arch/powerpc/include/asm/interrupt.h
> > +++ b/arch/powerpc/include/asm/interrupt.h
> > @@ -336,6 +336,16 @@ 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.
> > +        */
> > +#ifdef CONFIG_PPC64
> 
> Instead of adding this #ifdef in middle of code, could you define 
> is_embed_first_chunk as always 'true' when CONFIG_PPC64 is not defined ?

Will fix this in v3.

[...]
> > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> > index 2f19d5e944852..674b6e1bebe9a 100644
> > --- a/arch/powerpc/kernel/setup_64.c
> > +++ b/arch/powerpc/kernel/setup_64.c
> > @@ -834,6 +834,11 @@ static __init int pcpu_cpu_to_node(int cpu)
> > 
> >   unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
> >   EXPORT_SYMBOL(__per_cpu_offset);
> > +#ifdef CONFIG_JUMP_LABEL
> 
> Why this ifdef ? Even when CONFIG_JUMP_LABEL is not selected all this 
> should just work fine.

Yes you are right. I overlooked this. Will fix it in next revision.

Thanks for your review.

-- 
Mahesh J Salgaonkar