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Message-ID: <Y7w+r3Nbubin8sNN@hirez.programming.kicks-ass.net>
Date: Mon, 9 Jan 2023 17:19:59 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [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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