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

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 25/02/2022 à 11:24, Mahesh Salgaonkar a écrit :
> 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@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/interrupt.h |   15 +++++++++++++++
>   arch/powerpc/include/asm/percpu.h    |    2 ++
>   arch/powerpc/kernel/setup_64.c       |    3 +++
>   3 files changed, 20 insertions(+)


In file included from /linux/arch/powerpc/kernel/irq.c:57:0:
/linux/arch/powerpc/include/asm/interrupt.h: In function 
'interrupt_nmi_enter_prepare':
/linux/arch/powerpc/include/asm/interrupt.h:337:109: error: 
'__percpu_embed_first_chunk' undeclared (first use in this function)
/linux/arch/powerpc/include/asm/interrupt.h:337:109: note: each 
undeclared identifier is reported only once for each function it appears in
In file included from /linux/arch/powerpc/kernel/irq.c:57:0:
/linux/arch/powerpc/include/asm/interrupt.h: In function 
'interrupt_nmi_exit_prepare':
/linux/arch/powerpc/include/asm/interrupt.h:353:109: error: 
'__percpu_embed_first_chunk' undeclared (first use in this function)
In file included from /linux/arch/powerpc/kernel/irq.c:57:0:
/linux/arch/powerpc/include/asm/interrupt.h:366:1: error: label at end 
of compound statement
  skip_nmi_exit:
  ^
/linux/scripts/Makefile.build:288: recipe for target 
'arch/powerpc/kernel/irq.o' failed
make[3]: *** [arch/powerpc/kernel/irq.o] Error 1