Re: [PATCH v3] x86/kdump: Handle blocked NMIs interrupt to avoid kdump crashes

[Peter Zijlstra]

On Thu, Feb 02, 2023 at 09:40:53AM +0800, Zeng Heng wrote:
> If the cpu panics within the NMI interrupt context,
> there could be unhandled NMI interrupts in the
> background which are blocked by processor until
> next IRET instruction executes. Since that, it
> prevents nested execution of the NMI handler.
> 
> In case of IRET execution during kdump reboot and
> no proper NMIs handler registered at that point
> (such as during EFI loader), we need to handle these
> blocked NMI interrupts in advance to avoid kdump
> crashes.
> 
> Because asm_exc_nmi() has the ability to handle
> nested NMIs, here call iret_to_self() and execute
> IRET instruction in order to trigger and handle the
> possible blocked NMIs interrupts in advance before
> the IDT set invalidate.
> 
> Provide one of test case to reproduce the concerned
> issue, and here is the steps:
>   1. # cat uncorrected
>      CPU 1 BANK 4
>      STATUS uncorrected 0xc0
>      MCGSTATUS  EIPV MCIP
>      ADDR 0x1234
>      RIP 0xdeadbabe
>      RAISINGCPU 0
>      MCGCAP SER CMCI TES 0x6
>   2. # modprobe mce_inject
>   3. # mce-inject uncorrected
> 
> Mce-inject would trigger kernel panic under NMI
> interrupt context. In addition, we need another NMI
> interrupt raise (such as from watchdog) during panic
> process. Set proper watchdog threshold value and/or
> add an artificial delay to make sure watchdog interrupt
> raise during the panic procedure and the involved
> issue would occur.
> 
> Fixes: ca0e22d4f011 ("x86/boot/compressed/64: Always switch to own page table")
> Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
> ---
>   v1: add dummy NMI interrupt handler in EFI loader
>   v2: tidy up changelog, add comments (by Ingo Molnar)
>   v3: add iret_to_self() to deal with blocked NMIs in advance
> 
>  arch/x86/kernel/crash.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 305514431f26..3aaca680a639 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -41,6 +41,7 @@
>  #include <asm/intel_pt.h>
>  #include <asm/crash.h>
>  #include <asm/cmdline.h>
> +#include <asm/sync_core.h>
> 
>  /* Used while preparing memory map entries for second kernel */
>  struct crash_memmap_data {
> @@ -143,6 +144,19 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
> 
>  	crash_smp_send_stop();
> 
> +	/*
> +	 * If the cpu panics within the NMI interrupt context,
> +	 * there may be unhandled NMI interrupts which are
> +	 * blocked by processor until next IRET instruction
> +	 * executes.
> +	 *
> +	 * In case of IRET execution during kdump reboot and
> +	 * no proper NMIs handler registered at that point,
> +	 * we trigger and handle blocked NMIs in advance to
> +	 * avoid kdump crashes.
> +	 */
> +	iret_to_self();
> +
>  	/*
>  	 * VMCLEAR VMCSs loaded on this cpu if needed.
>  	 */

I never remember the shutdown paths -- do we force wipe the PMU
registers somewhere before this?