linux-kernel - [PATCH] x86, 64bit: Always make MAX

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Date:	Thu, 30 Dec 2010 17:05:17 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, 64bit: Always make MAX_APICS to 32768

Found one x2apic pre-enabled system, x2apic_mode suddenly get corrupted
after register some cpus. when compiled CONFIG_NR_CPUS=255 instead of 512

It turns out that generic_processor_info() ==> phyid_set(apicid, phys_cpu_present_map) cause the problem.

phys_cpu_present_map is with MAX_APICS bits. and pre-enabled system some cpus apic id > 255.

the variable after phys_cpu_present_map may get corrupted.... siliently...

ffffffff828e8420 B phys_cpu_present_map
ffffffff828e8440 B apic_verbosity
ffffffff828e8444 B local_apic_timer_c2_ok
ffffffff828e8448 B disable_apic
ffffffff828e844c B x2apic_mode
ffffffff828e8450 B x2apic_disabled
ffffffff828e8454 B num_processors
...

Actually phys_cpu_present_map is referenced via apic id, instead index. we should use
MAX_LOCAL_APIC instead MAX_APICIS. but that is another header.

So just let MAX_APICS equal to MAX_LOCAL_APIC at this point.
esp for 64 bit will be 32768 in all cases.

Signed-off-by: Yinghai Lu <yinghai@...nel.org>

---
 arch/x86/include/asm/mpspec_def.h |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Index: linux-2.6/arch/x86/include/asm/mpspec_def.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/mpspec_def.h
+++ linux-2.6/arch/x86/include/asm/mpspec_def.h
@@ -17,11 +17,7 @@
 # define MAX_MPC_ENTRY 1024
 # define MAX_APICS      256
 #else
-# if NR_CPUS <= 255
-#  define MAX_APICS     255
-# else
-#  define MAX_APICS   32768
-# endif
+# define MAX_APICS    32768
 #endif

 /* Intel MP Floating Pointer Structure */
--
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