(2013/10/16 4:12), Vivek Goyal wrote:
On Tue, Oct 15, 2013 at 02:43:22PM +0900, HATAYAMA Daisuke wrote:
Kexec can enter the kdump 2nd kernel on AP if crash happens on AP. To
check if boot cpu is BSP, introduce a helper function
boot_cpu_is_bsp().
Signed-off-by: HATAYAMA Daisuke <d.hatay...@jp.fujitsu.com>
---
arch/x86/include/asm/mpspec.h | 7 +++++++
arch/x86/kernel/apic/apic.c | 16 ++++++++++++++++
arch/x86/kernel/setup.c | 2 ++
3 files changed, 25 insertions(+)
diff --git a/arch/x86/include/asm/mpspec.h b/arch/x86/include/asm/mpspec.h
index 626cf70..54d5f98 100644
--- a/arch/x86/include/asm/mpspec.h
+++ b/arch/x86/include/asm/mpspec.h
@@ -47,11 +47,18 @@ extern int mp_bus_id_to_type[MAX_MP_BUSSES];
extern DECLARE_BITMAP(mp_bus_not_pci, MAX_MP_BUSSES);
extern unsigned int boot_cpu_physical_apicid;
+extern bool boot_cpu_is_bsp;
extern unsigned int max_physical_apicid;
extern int mpc_default_type;
extern unsigned long mp_lapic_addr;
#ifdef CONFIG_X86_LOCAL_APIC
+extern void boot_cpu_is_bsp_init(void);
+#else
+static inline void boot_cpu_is_bsp_init(void) { };
+#endif
+
+#ifdef CONFIG_X86_LOCAL_APIC
extern int smp_found_config;
#else
# define smp_found_config 0
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index a7eb82d..62ee365 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -64,6 +64,12 @@ unsigned disabled_cpus;
unsigned int boot_cpu_physical_apicid = -1U;
/*
[..]
+ * Indicates whether the processor that is doing the boot up, is BSP
+ * processor or not.
+ */
+bool boot_cpu_is_bsp;
Should we set it to true by default? I think in most of the cases boot cpu
is going to be bsp too?
Agreed. Most likely value should be default.
The reason why I wrote so would be that -- if there's reason -- I wanted to
write it uniform to other variables around it and wanted to avoid to let it
have static storage in binary file.
+
+/*
* The highest APIC ID seen during enumeration.
*/
unsigned int max_physical_apicid;
@@ -2589,3 +2595,13 @@ static int __init lapic_insert_resource(void)
* that is using request_resource
*/
late_initcall(lapic_insert_resource);
+
+void __init boot_cpu_is_bsp_init(void)
+{
+ if (cpu_has_apic) {
+ u32 l, h;
+
+ rdmsr_safe(MSR_IA32_APICBASE, &l, &h);
+ boot_cpu_is_bsp = (l & MSR_IA32_APICBASE_BSP) ? true : false;
I came across following thread.
https://lkml.org/lkml/2012/4/18/370
Can we hit above read msr on old P5 class machines? Or is it safe to
call unconditionally.
No, it's dangerous to cause #UD, and current implementation doesn't check
exception value returned by rdmsr_safe. It's meaningless to call rdmsr_safe.
At least, checking boot_cpu_data.x86 >= 6 satisfies support of IA32_APIC_BASE
MSR and this at the same time satisfies support of rdmsr instruction since the
instruction was introduced at Pentium processor. So,
if (boot_cpu_data.x86 >= 6 && cpu_has_apic()) {
u32 l, h;
rdmsr(MSR_IA32_APICBASE, &l, &h);
boot_cpu_is_bsp = (l & MSR_IA32_APICBASE_BSP) ? true : false;
}
--
Thanks.
HATAYAMA, Daisuke
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