x86, x2apic: Fallback to xapic when BIOS doesn't setup interrupt-remapping
On some of the recent Intel SNB platforms, by default bios is pre-enabling
x2apic mode in the cpu with out setting up interrupt-remapping.
This case was resulting in the kernel to panic as the cpu is already in
x2apic mode but the OS was not able to enable interrupt-remapping (which
is a pre-req for using x2apic capability).
On these platforms all the apic-ids are < 255 and the kernel can fallback to
xapic mode if the bios has not enabled interrupt-remapping (which is
mostly the case if the bios has not exported interrupt-remapping tables to the
OS).
Reported-by: Berck E. Nash <flyboy@gmail.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/20111222014632.600418637@sbsiddha-desk.sc.intel.com
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index a0f541a..a12d571 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -176,6 +176,7 @@
}
extern int x2apic_phys;
+extern int x2apic_preenabled;
extern void check_x2apic(void);
extern void enable_x2apic(void);
extern void x2apic_icr_write(u32 low, u32 id);
@@ -198,6 +199,9 @@
x2apic_phys = 1;
}
#else
+static inline void disable_x2apic(void)
+{
+}
static inline void check_x2apic(void)
{
}