From: Prarit Bhargava <prarit@redhat.com>
Date: Tue, 22 Sep 2009 11:20:31 -0400
Subject: [x86] fix nosmp option
Message-id: 4AB8EB3F.1080003@redhat.com
O-Subject: Re: [RHEL5 PATCH] fix nosmp option
Bugzilla: 509581
RH-Acked-by: Chris Lalancette <clalance@redhat.com>
RH-Acked-by: Stefan Assmann <sassmann@redhat.com>
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>

nosmp should not enable the IOAPIC.

This causes spurious interrupts to occur, and in some cases, the system will
panic when the nosmp option is enabled.

Successfully tested by me as well as the customer.

Resolves BZ 509581.

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 43512d0..46a2755 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -963,7 +963,10 @@ running once the system is up.
 			Format: <1-256>
 
 	maxcpus=	[SMP] Maximum number of processors that	an SMP kernel
-			should make use of
+			should make use of.  maxcpus=n : n >= 0 limits the
+			kernel to using 'n' processors.  n=0 is a special case,
+			it is equivalent to "nosmp", which also disables
+			the IO APIC.
 
 	max_addr=[KMG]	[KNL,BOOT,ia64] All physical memory greater than or
 			equal to this physical address is ignored.
@@ -1217,7 +1220,8 @@ running once the system is up.
 
 	nosep		[BUGS=IA-32] Disables x86 SYSENTER/SYSEXIT support.
 
-	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel.
+	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
+			and disable the IO APIC.  legacy for "maxcpus=0".
 
 	nosync		[HW,M68K] Disables sync negotiation for all devices.
 
diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 84889d1..2364d1d 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -691,14 +691,6 @@ static int pirq_entries [MAX_PIRQS];
 static int pirqs_enabled;
 int skip_ioapic_setup;
 
-static int __init ioapic_setup(char *str)
-{
-	skip_ioapic_setup = 1;
-	return 1;
-}
-
-__setup("noapic", ioapic_setup);
-
 static int __init ioapic_pirq_setup(char *str)
 {
 	int i, max;
diff --git a/arch/i386/kernel/setup.c b/arch/i386/kernel/setup.c
index 7d00734..dcb5564 100644
--- a/arch/i386/kernel/setup.c
+++ b/arch/i386/kernel/setup.c
@@ -957,6 +957,8 @@ static void __init parse_cmdline_early (char ** cmdline_p)
 
 		else if (!memcmp(from, "ipmi_dev_order=", 15))
 			ipmi_dev_order = simple_strtoul(from + 15, NULL, 0);
+		else if (!memcmp(from, "nosmp", 5))
+			nosmp(NULL);
 
 	next_char:
 		c = *(from++);
diff --git a/arch/x86_64/kernel/io_apic-xen.c b/arch/x86_64/kernel/io_apic-xen.c
index b47bcee..91f19de 100644
--- a/arch/x86_64/kernel/io_apic-xen.c
+++ b/arch/x86_64/kernel/io_apic-xen.c
@@ -284,11 +284,9 @@ static int pirqs_enabled;
 int skip_ioapic_setup;
 int ioapic_force;
 
-/* dummy parsing: see setup.c */
-
-static int __init disable_ioapic_setup(char *str)
+static int __init parse_noapic(char *str)
 {
-	skip_ioapic_setup = 1;
+	disable_ioapic_setup();
 	return 1;
 }
 
@@ -299,7 +297,7 @@ static int __init enable_ioapic_setup(char *str)
 	return 1;
 }
 
-__setup("noapic", disable_ioapic_setup);
+__setup("noapic", parse_noapic);
 __setup("apic", enable_ioapic_setup);
 
 #ifndef CONFIG_XEN
diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
index 3caf95d..9a764b9 100644
--- a/arch/x86_64/kernel/io_apic.c
+++ b/arch/x86_64/kernel/io_apic.c
@@ -242,11 +242,9 @@ static int pirqs_enabled;
 int skip_ioapic_setup;
 int ioapic_force;
 
-/* dummy parsing: see setup.c */
-
-static int __init disable_ioapic_setup(char *str)
+static int __init parse_noapic(char *str)
 {
-	skip_ioapic_setup = 1;
+	disable_ioapic_setup();
 	return 1;
 }
 
@@ -257,7 +255,7 @@ static int __init enable_ioapic_setup(char *str)
 	return 1;
 }
 
-__setup("noapic", disable_ioapic_setup);
+__setup("noapic", parse_noapic);
 __setup("apic", enable_ioapic_setup);
 
 static int __init setup_disable_8254_timer(char *s)
diff --git a/arch/x86_64/kernel/setup-xen.c b/arch/x86_64/kernel/setup-xen.c
index 3758b68..72f73ed 100644
--- a/arch/x86_64/kernel/setup-xen.c
+++ b/arch/x86_64/kernel/setup-xen.c
@@ -504,6 +504,8 @@ static __init void parse_cmdline_early (char ** cmdline_p)
 
 		else if (!memcmp(from, "ipmi_dev_order=", 15))
 			ipmi_dev_order = simple_strtoul(from + 15, NULL, 0);
+		else if (!memcmp(from, "nosmp", 5))
+			nosmp(NULL);
 
 	next_char:
 		c = *(from++);
diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 7a6f5e9..8a35974 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -433,6 +433,8 @@ static __init void parse_cmdline_early (char ** cmdline_p)
 
 		else if (!memcmp(from, "ipmi_dev_order=", 15))
 			ipmi_dev_order = simple_strtoul(from + 15, NULL, 0);
+		else if (!memcmp(from, "nosmp", 5))
+			nosmp(NULL);
 
 	next_char:
 		c = *(from++);
diff --git a/include/asm-x86_64/io_apic.h b/include/asm-x86_64/io_apic.h
index 9a81eaf..f342532 100644
--- a/include/asm-x86_64/io_apic.h
+++ b/include/asm-x86_64/io_apic.h
@@ -183,6 +183,12 @@ static inline void io_apic_sync(unsigned int apic)
 /* 1 if "noapic" boot option passed */
 extern int skip_ioapic_setup;
 
+static inline void disable_ioapic_setup(void)
+{
+	skip_ioapic_setup = 1;
+}
+
+
 /*
  * If we use the IO-APIC for IRQ routing, disable automatic
  * assignment of PCI IRQ's.
diff --git a/include/linux/init.h b/include/linux/init.h
index 263120d..772dddf 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -155,6 +155,7 @@ struct obs_kernel_param {
 
 /* Relies on saved_command_line being set */
 void __init parse_early_param(void);
+int __init nosmp(char *str);
 #endif /* __ASSEMBLY__ */
 
 /**
diff --git a/init/main.c b/init/main.c
index 06349fe..3d0e873 100644
--- a/init/main.c
+++ b/init/main.c
@@ -149,12 +149,15 @@ EXPORT_SYMBOL(reset_devices);
  * greater than 0, limits the maximum number of CPUs activated in
  * SMP mode to <NUM>.
  */
-static int __init nosmp(char *str)
+#ifndef CONFIG_X86_IO_APIC
+static inline void disable_ioapic_setup(void) {};
+#endif
+int __init nosmp(char *str)
 {
 	max_cpus = 0;
+	disable_ioapic_setup();
 	return 1;
 }
-
 __setup("nosmp", nosmp);
 
 static int __init maxcpus(char *str)