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powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

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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.

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Shirisha Ganta <shirisha@linux.ibm.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240410043006.81577-1-mahesh@linux.ibm.com
This commit is contained in:
Mahesh Salgaonkar 2024-04-10 10:00:06 +05:30 committed by Michael Ellerman
parent 676b2f99b0
commit 0db880fc86
3 changed files with 22 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
arch/powerpc/include/asm/interrupt.h
View File

@ -336,6 +336,14 @@ static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, struct inte
if (IS_ENABLED(CONFIG_KASAN)) if (IS_ENABLED(CONFIG_KASAN))
return; 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 (percpu_first_chunk_is_paged)
return;
/* Otherwise, it should be safe to call it */ /* Otherwise, it should be safe to call it */
nmi_enter(); 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 // no nmi_exit for a pseries hash guest taking a real mode exception
} else if (IS_ENABLED(CONFIG_KASAN)) { } else if (IS_ENABLED(CONFIG_KASAN)) {
// no nmi_exit for KASAN in real mode // no nmi_exit for KASAN in real mode
} else if (percpu_first_chunk_is_paged) {
// no nmi_exit if percpu first chunk is not embedded
} else { } else {
nmi_exit(); nmi_exit();
} }

10
arch/powerpc/include/asm/percpu.h
View File

@ -15,6 +15,16 @@
#endif /* CONFIG_SMP */ #endif /* CONFIG_SMP */
#endif /* __powerpc64__ */ #endif /* __powerpc64__ */
#if defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && defined(CONFIG_SMP)
#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 && CONFIG_SMP */
#include <asm-generic/percpu.h> #include <asm-generic/percpu.h>
#include <asm/paca.h> #include <asm/paca.h>

2
arch/powerpc/kernel/setup_64.c
View File

@ -834,6 +834,7 @@ static __init int pcpu_cpu_to_node(int cpu)
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly; unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
EXPORT_SYMBOL(__per_cpu_offset); EXPORT_SYMBOL(__per_cpu_offset);
DEFINE_STATIC_KEY_FALSE(__percpu_first_chunk_is_paged);
void __init setup_per_cpu_areas(void) void __init setup_per_cpu_areas(void)
{ {
@ -876,6 +877,7 @@ void __init setup_per_cpu_areas(void)
if (rc < 0) if (rc < 0)
panic("cannot initialize percpu area (err=%d)", rc); panic("cannot initialize percpu area (err=%d)", rc);
static_key_enable(&__percpu_first_chunk_is_paged.key);
delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start; delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
for_each_possible_cpu(cpu) { for_each_possible_cpu(cpu) {
__per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu]; __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];