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powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.
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 <[email protected]> Tested-by: Shirisha Ganta <[email protected]> Signed-off-by: Mahesh Salgaonkar <[email protected]> --- Changes in v5: - Invert the percpu chunk checks as suggested by mpe. - Fix mirowatt build, microwatt config has CONFIG_PPC64=y and CONFIG_SMP=n - v4 at https://lore.kernel.org/linuxppc-dev/[email protected]/ Changes in v4: - Fix coding style issues. Changes in v3: - Address comments from Christophe Leroy to avoid using #ifdefs in the code - v2 at https://lore.kernel.org/linuxppc-dev/[email protected]/ 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/
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