[PATCH v3] powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

[Christophe Leroy]

Le 14/02/2024 à 10:16, Mahesh Salgaonkar a écrit :
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> 
> 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 v3:
> - Address comments from Christophe Leroy to avoid using #ifdefs in the
>    code
> - v2 at https://lore.kernel.org/linuxppc-dev/20240205053647.1763446-1-mahesh@linux.ibm.com/
> 
> Changes in v2:
> - Rebase to upstream master
> - Use jump_labels, if CONFIG_JUMP_LABEL is enabled, to avoid redoing the
>    embed first chunk 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 | 10 ++++++++++
>   arch/powerpc/include/asm/percpu.h    | 10 ++++++++++
>   arch/powerpc/kernel/setup_64.c       |  4 ++++
>   3 files changed, 24 insertions(+)
> 
> 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)
> +               return;
> +
>          /* Otherwise, it should be safe to call it */
>          nmi_enter();
>   }
> @@ -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..d1fdf25897dc1 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)

Parenthesis aroud true are not necessary

> +#endif /* CONFIG_PPC64 */
> +
>   #include <asm-generic/percpu.h>
> 
>   #include <asm/paca.h>
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 2f19d5e944852..cbd3b4c82316c 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 +870,9 @@ 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);
> +               }

Braces are unnecessary for single line, in addition it adds unbalanced 
bracing as the first leg doesn't have braces, see 
https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces

>          }
> 
>          if (rc < 0)
> --
> 2.43.0
>