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 <mah...@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-mah...@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) +#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); + } } if (rc < 0) -- 2.43.0
