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SubjectRe: [PATCH x86/nmi 1/2] x86/nmi: Accumulate NMI-progress evidence in exc_nmi()
On Wed, Jan 04, 2023 at 05:15:36PM -0800, Paul E. McKenney wrote:

> diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
> index cec0bfa3bc04f..4f1651dc65b3a 100644
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -69,6 +69,15 @@ struct nmi_stats {
> unsigned int unknown;
> unsigned int external;
> unsigned int swallow;
> + unsigned long recv_jiffies;
> + unsigned long idt_seq;
> + unsigned long idt_nmi_seq;
> + unsigned long idt_ignored;
> + atomic_long_t idt_calls;
> + unsigned long idt_seq_snap;
> + unsigned long idt_nmi_seq_snap;
> + unsigned long idt_ignored_snap;
> + long idt_calls_snap;
> };

Urgh, this is more than a whole cacheline of extra data :/ Can't we make
this #ifdef CONFIG_NMI_CHECK_CPU ?

> @@ -509,8 +526,15 @@ DEFINE_IDTENTRY_RAW(exc_nmi)
>
> inc_irq_stat(__nmi_count);
>
> - if (!ignore_nmis)
> + if (IS_ENABLED(CONFIG_NMI_CHECK_CPU) && ignore_nmis) {
> + WRITE_ONCE(nsp->idt_ignored, nsp->idt_ignored + 1);
> + } else if (!ignore_nmis) {
> + WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1);
> + WARN_ON_ONCE(!(nsp->idt_nmi_seq & 0x1));
> default_do_nmi(regs);
> + WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1);
> + WARN_ON_ONCE(nsp->idt_nmi_seq & 0x1);
> + }
>
> irqentry_nmi_exit(regs, irq_state);

That is not a NO-OP when !CONFIG_NMI_CHECK_CPU :/

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