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Date: Mon, 21 Mar 2011 11:56:08 -0500
From: Jack Steiner <steiner@....com>
To: Ingo Molnar <mingo@...e.hu>
Cc: tglx@...utronix.de, hpa@...or.com, x86@...nel.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: [PATCH] x86, UV: Fix NMI handler for UV platforms
On Mon, Mar 21, 2011 at 05:14:25PM +0100, Ingo Molnar wrote:
>
> * Jack Steiner <steiner@....com> wrote:
>
> > This fixes a problem seen on UV systems handling NMIs from the node controller.
> > The original code used the DIE notifier as the hook to get to the UV NMI
> > handler. This does not work if performance counters are active - the hw_perf
> > code consumes the NMI and the UV handler is not called.
>
> Sigh:
Agree. X86 architecture does not make it easy to use NMIs from multiple sources.
>
> > --- linux.orig/arch/x86/kernel/traps.c 2011-03-21 09:05:43.000000000 -0500
> > +++ linux/arch/x86/kernel/traps.c 2011-03-21 09:13:01.306555675 -0500
> > @@ -57,6 +57,7 @@
> > #include <asm/mce.h>
> >
> > #include <asm/mach_traps.h>
> > +#include <asm/uv/uv.h>
> >
> > #ifdef CONFIG_X86_64
> > #include <asm/x86_init.h>
> > @@ -397,13 +398,16 @@ unknown_nmi_error(unsigned char reason,
> > static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
> > {
> > unsigned char reason = 0;
> > + int handled;
> >
> > /*
> > * 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 (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
> > + handled = uv_handle_nmi(regs, reason);
> > + if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP ||
> > + handled)
> > return;
>
> Such code is extremely ugly. Please *reduce* the number of is_uv_system() type
> of hacks in core x86 code, not increase it!
>
> Any reason why a higher priority for the UV NMI handler cannot solve the 'perf
> eats the NMI' problem?
Yes. I tried that.
If the UV handler needs to know if hwperf is active in order to know whether or not
to return NOTIFY_STOP:
- if the UV NMI handler returns NOTIFY_STOP and hw_perf is active, hw_perf will miss
and NMI & counter sometimes stop working.
- if the UV NMI handler does not return NOTIFY_STOP and hw_perf is not active,
we get the "dazed" messages.
A cleaner solution would be to hide the platform specific NMI action in a x86_platform_ops
such as (untested):
Index: linux/arch/x86/include/asm/x86_init.h
===================================================================
--- linux.orig/arch/x86/include/asm/x86_init.h 2011-03-18 11:29:08.000000000 -0500
+++ linux/arch/x86/include/asm/x86_init.h 2011-03-21 11:52:36.413496546 -0500
@@ -153,6 +153,7 @@ struct x86_platform_ops {
void (*iommu_shutdown)(void);
bool (*is_untracked_pat_range)(u64 start, u64 end);
void (*nmi_init)(void);
+ int (*nmi_handler)(void *regs);
int (*i8042_detect)(void);
};
Index: linux/arch/x86/kernel/apic/x2apic_uv_x.c
===================================================================
--- linux.orig/arch/x86/kernel/apic/x2apic_uv_x.c 2011-03-21 11:40:36.000000000 -0500
+++ linux/arch/x86/kernel/apic/x2apic_uv_x.c 2011-03-21 11:45:14.134555108 -0500
@@ -115,6 +115,7 @@ static int __init uv_acpi_madt_oem_check
early_get_apic_pnode_shift();
x86_platform.is_untracked_pat_range = uv_is_untracked_pat_range;
x86_platform.nmi_init = uv_nmi_init;
+ x86_platform.nmi_handler = uv_nmi_handler;
if (!strcmp(oem_table_id, "UVL"))
uv_system_type = UV_LEGACY_APIC;
else if (!strcmp(oem_table_id, "UVX"))
Index: linux/arch/x86/kernel/traps.c
===================================================================
--- linux.orig/arch/x86/kernel/traps.c 2011-03-21 11:40:36.000000000 -0500
+++ linux/arch/x86/kernel/traps.c 2011-03-21 11:52:21.057498053 -0500
@@ -55,6 +55,8 @@
#include <asm/desc.h>
#include <asm/i387.h>
#include <asm/mce.h>
+#include <asm/x86_init.h>
+
#include <asm/mach_traps.h>
@@ -397,13 +399,16 @@ unknown_nmi_error(unsigned char reason,
static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
{
unsigned char reason = 0;
+ int handled;
/*
* 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 (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
+ handled = x86_platform.nmi_handler(regs);
+ if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP ||
+ handled)
return;
/* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
Index: linux/arch/x86/kernel/x86_init.c
===================================================================
--- linux.orig/arch/x86/kernel/x86_init.c 2011-03-18 11:29:08.000000000 -0500
+++ linux/arch/x86/kernel/x86_init.c 2011-03-21 11:53:26.849496085 -0500
@@ -89,6 +89,7 @@ struct x86_cpuinit_ops x86_cpuinit __cpu
};
static void default_nmi_init(void) { };
+static int default_nmi_handler(void *regs) { return 1; };
static int default_i8042_detect(void) { return 1; };
struct x86_platform_ops x86_platform = {
@@ -98,6 +99,7 @@ struct x86_platform_ops x86_platform = {
.iommu_shutdown = iommu_shutdown_noop,
.is_untracked_pat_range = is_ISA_range,
.nmi_init = default_nmi_init,
+ .nmi_handler = default_nmi_handler,
.i8042_detect = default_i8042_detect
};
--
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