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x86: Ignore NMIs that come in during early boot
Don Zickus reports: A customer generated an external NMI using their iLO to test kdump worked. Unfortunately, the machine hung. Disabling the nmi_watchdog made things work. I speculated the external NMI fired, caused the machine to panic (as expected) and the perf NMI from the watchdog came in and was latched. My guess was this somehow caused the hang. ---- It appears that the latched NMI stays latched until the early page table generation on 64 bits, which causes exceptions to happen which end in IRET, which re-enable NMI. Therefore, ignore NMIs that come in during early execution, until we have proper exception handling. Reported-and-tested-by: Don Zickus <dzickus@redhat.com> Link: http://lkml.kernel.org/r/1394221143-29713-1-git-send-email-dzickus@redhat.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: <stable@vger.kernel.org> # v3.5+, older with some backport effort
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2 changed files with 11 additions and 2 deletions
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@ -544,6 +544,10 @@ ENDPROC(early_idt_handlers)
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/* This is global to keep gas from relaxing the jumps */
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ENTRY(early_idt_handler)
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cld
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cmpl $X86_TRAP_NMI,(%esp)
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je is_nmi # Ignore NMI
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cmpl $2,%ss:early_recursion_flag
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je hlt_loop
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incl %ss:early_recursion_flag
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@ -594,8 +598,9 @@ ex_entry:
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pop %edx
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pop %ecx
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pop %eax
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addl $8,%esp /* drop vector number and error code */
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decl %ss:early_recursion_flag
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is_nmi:
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addl $8,%esp /* drop vector number and error code */
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iret
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ENDPROC(early_idt_handler)
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@ -343,6 +343,9 @@ early_idt_handlers:
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ENTRY(early_idt_handler)
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cld
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cmpl $X86_TRAP_NMI,(%rsp)
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je is_nmi # Ignore NMI
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cmpl $2,early_recursion_flag(%rip)
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jz 1f
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incl early_recursion_flag(%rip)
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@ -405,8 +408,9 @@ ENTRY(early_idt_handler)
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popq %rdx
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popq %rcx
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popq %rax
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addq $16,%rsp # drop vector number and error code
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decl early_recursion_flag(%rip)
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is_nmi:
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addq $16,%rsp # drop vector number and error code
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INTERRUPT_RETURN
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ENDPROC(early_idt_handler)
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