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Date: Mon, 27 Sep 2010 11:41:36 +0200
From: Robert Richter <robert.richter@....com>
To: Huang Ying <ying.huang@...el.com>
CC: Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
"H. Peter Anvin" <hpa@...or.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v2 4/7] x86, NMI, Rewrite NMI handler
On 26.09.10 20:57:03, Huang Ying wrote:
> The original NMI handler is quite outdated in many aspects. This patch
> try to fix it.
>
> The order to process the NMI sources are changed as follow:
>
> notify_die(DIE_NMI_IPI);
> notify_die(DIE_NMI);
> /* process io port 0x61 */
> nmi_watchdog_touch();
> notify_die(DIE_NMIUNKNOWN);
> unknown_nmi();
>
> DIE_NMI_IPI is used to process CPU specific NMI sources, such as perf
> event, oprofile, crash IPI, etc. While DIE_NMI is used to process
> non-CPU-specific NMI sources, such as APEI (ACPI Platform Error
> Interface) GHES (Generic Hardware Error Source), etc. Non-CPU-specific
> NMI sources can be processed on any CPU,
>
> DIE_NMI_IPI must be processed before DIE_NMI. For example, perf event
> trigger a NMI on CPU 1, at the same time, APEI GHES trigger another
> NMI on CPU 0. If DIE_NMI is processed before DIE_NMI_IPI, it is
> possible that APEI GHES is processed on CPU 1, while unknown NMI is
> gotten on CPU 0.
I think macro names DIE_NMI_IPI and DIE_NMI should be swapped as
e.g. the perf nmi is actually local and non-IPI.
We might consider to rework the IPI thing completly, but may be in a
follow-on patch.
>
> In this new order of processing, performance sensitive NMI sources
> such as oprofile or perf event will have better performance because
> the time consuming IO port reading is done after them.
>
> Only one NMI is eaten for each NMI handler call, even for PCI SERR and
> IOCHK NMIs. Because one NMI should be raised for each of them, eating
> too many NMI will cause unnecessary unknown NMI.
>
> The die value used in NMI sources are fixed accordingly.
>
> The NMI handler in the patch is designed by Andi Kleen.
>
>
> v2:
>
> - Split process NMI reason (0x61) on non-BSP into another patch
>
> Signed-off-by: Huang Ying <ying.huang@...el.com>
> ---
> arch/x86/kernel/cpu/perf_event.c | 1
> arch/x86/kernel/traps.c | 80 +++++++++++++++++++-------------------
> arch/x86/oprofile/nmi_int.c | 1
> arch/x86/oprofile/nmi_timer_int.c | 2
> drivers/char/ipmi/ipmi_watchdog.c | 2
> drivers/watchdog/hpwdt.c | 2
> 6 files changed, 43 insertions(+), 45 deletions(-)
>
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1247,7 +1247,6 @@ perf_event_nmi_handler(struct notifier_b
> return NOTIFY_DONE;
>
> switch (cmd) {
> - case DIE_NMI:
> case DIE_NMI_IPI:
See my comment above. Same is true for oprofile and some other
handlers below. It isn't an IPI and should be case DIE_NMI: instead.
> break;
> case DIE_NMIUNKNOWN:
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -354,9 +354,6 @@ io_check_error(unsigned char reason, str
> static notrace __kprobes void
> unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
> {
> - if (notify_die(DIE_NMIUNKNOWN, "nmi", regs, reason, 2, SIGINT) ==
> - NOTIFY_STOP)
> - return;
> #ifdef CONFIG_MCA
> /*
> * Might actually be able to figure out what the guilty party
> @@ -385,51 +382,54 @@ static notrace __kprobes void default_do
>
> cpu = smp_processor_id();
This should go to if (!cpu) and maybe we drop variable cpu completly.
>
> - /* Only the BSP gets external NMIs from the system. */
> - if (!cpu)
> - reason = get_nmi_reason();
> + /*
> + * CPU-specific NMI must be processed before non-CPU-specific
> + * NMI, otherwise we may lose it, because the CPU-specific
> + * NMI can not be detected/processed on other CPUs.
> + */
>
> - if (!(reason & NMI_REASON_MASK)) {
> - if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 2, SIGINT)
> - == NOTIFY_STOP)
> - return;
> + /*
> + * CPU-specific NMI: send to specific CPU or NMI sources must
> + * be processed on specific CPU
> + */
> + if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, 0, 2, SIGINT)
> + == NOTIFY_STOP)
> + return;
>
> -#ifdef CONFIG_X86_LOCAL_APIC
Are you sure we may drop this option?
> - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
> - == NOTIFY_STOP)
> - return;
> + /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
> + if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
> + return;
As said, IPI and non-IPI are mixed up.
>
> -#ifndef CONFIG_LOCKUP_DETECTOR
> - /*
> - * Ok, so this is none of the documented NMI sources,
> - * so it must be the NMI watchdog.
> - */
> - if (nmi_watchdog_tick(regs, reason))
> - return;
> - if (!do_nmi_callback(regs, cpu))
> -#endif /* !CONFIG_LOCKUP_DETECTOR */
> - unknown_nmi_error(reason, regs);
> -#else
> - unknown_nmi_error(reason, regs);
> + if (!cpu) {
> + reason = get_nmi_reason();
> + if (reason & NMI_REASON_MASK) {
> + if (reason & NMI_REASON_SERR)
> + pci_serr_error(reason, regs);
> + else if (reason & NMI_REASON_IOCHK)
> + io_check_error(reason, regs);
> +#ifdef CONFIG_X86_32
> + /*
> + * Reassert NMI in case it became active
> + * meanwhile as it's edge-triggered:
> + */
> + reassert_nmi();
> #endif
> + return;
> + }
> + }
>
> +#if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
> + if (nmi_watchdog_tick(regs, reason))
> return;
> - }
> - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT) == NOTIFY_STOP)
> + if (do_nmi_callback(regs, smp_processor_id()))
> return;
> -
> - /* AK: following checks seem to be broken on modern chipsets. FIXME */
> - if (reason & NMI_REASON_SERR)
> - pci_serr_error(reason, regs);
> - if (reason & NMI_REASON_IOCHK)
> - io_check_error(reason, regs);
> -#ifdef CONFIG_X86_32
> - /*
> - * Reassert NMI in case it became active meanwhile
> - * as it's edge-triggered:
> - */
> - reassert_nmi();
> #endif
> +
> + if (notify_die(DIE_NMIUNKNOWN, "nmi_unknown", regs, reason, 2, SIGINT)
> + == NOTIFY_STOP)
> + return;
> +
> + unknown_nmi_error(reason, regs);
> }
>
> dotraplinkage notrace __kprobes void
> --- a/arch/x86/oprofile/nmi_int.c
> +++ b/arch/x86/oprofile/nmi_int.c
> @@ -64,7 +64,6 @@ static int profile_exceptions_notify(str
> int ret = NOTIFY_DONE;
>
> switch (val) {
> - case DIE_NMI:
> case DIE_NMI_IPI:
> if (ctr_running)
> model->check_ctrs(args->regs, &__get_cpu_var(cpu_msrs));
> --- a/arch/x86/oprofile/nmi_timer_int.c
> +++ b/arch/x86/oprofile/nmi_timer_int.c
> @@ -25,7 +25,7 @@ static int profile_timer_exceptions_noti
> int ret = NOTIFY_DONE;
>
> switch (val) {
> - case DIE_NMI:
> + case DIE_NMI_IPI:
> oprofile_add_sample(args->regs, 0);
> ret = NOTIFY_STOP;
> break;
> --- a/drivers/char/ipmi/ipmi_watchdog.c
> +++ b/drivers/char/ipmi/ipmi_watchdog.c
> @@ -1080,7 +1080,7 @@ ipmi_nmi(struct notifier_block *self, un
> {
> struct die_args *args = data;
>
> - if (val != DIE_NMI)
> + if (val != DIE_NMIUNKNOWN)
As this function handles an nmi and not an unknown nmi, we should keep
DIE_NMI here and better modify priorities in ipmi_nmi_handler.
> return NOTIFY_OK;
>
> /* Hack, if it's a memory or I/O error, ignore it. */
> --- a/drivers/watchdog/hpwdt.c
> +++ b/drivers/watchdog/hpwdt.c
> @@ -469,7 +469,7 @@ static int hpwdt_pretimeout(struct notif
> unsigned long rom_pl;
> static int die_nmi_called;
>
> - if (ulReason != DIE_NMI && ulReason != DIE_NMI_IPI)
> + if (ulReason != DIE_NMIUNKNOWN)
Same here, but dropping DIE_NMI_IPI.
-Robert
> goto out;
>
> if (!hpwdt_nmi_decoding)
> --
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--
Advanced Micro Devices, Inc.
Operating System Research Center
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