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 a0f541a309448f3ecd8eb3b1f48098a4ffbea6d6..a12d57193fef7b22e33649153e37005c56f11b6b 100644 (file)
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -176,6 +176,7 @@ static inline u64 native_x2apic_icr_read(void)
 }
 
 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 @@ static inline void x2apic_force_phys(void)
        x2apic_phys = 1;
 }
 #else
+static inline void disable_x2apic(void)
+{
+}
 static inline void check_x2apic(void)
 {
 }

diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
index 3925d80078642d76f1890202d55037e9442b3f03..134bba00df09db0ebc3c6b6a0fa091cd367e1e3c 100644 (file)
--- a/arch/x86/include/asm/apicdef.h
+++ b/arch/x86/include/asm/apicdef.h
@@ -144,6 +144,7 @@
 
 #define APIC_BASE (fix_to_virt(FIX_APIC_BASE))
 #define APIC_BASE_MSR  0x800
+#define XAPIC_ENABLE   (1UL << 11)
 #define X2APIC_ENABLE  (1UL << 10)
 
 #ifdef CONFIG_X86_32

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 07832363b729846ddd7eac0e92ca65c5a608d0be..2c07aebbb6f2e790c6b730946fb62609c9f85d3c 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -146,7 +146,8 @@ __setup("apicpmtimer", setup_apicpmtimer);
 int x2apic_mode;
 #ifdef CONFIG_X86_X2APIC
 /* x2apic enabled before OS handover */
-static int x2apic_preenabled;
+int x2apic_preenabled;
+static int x2apic_disabled;
 static __init int setup_nox2apic(char *str)
 {
        if (x2apic_enabled()) {
@@ -1432,6 +1433,40 @@ void __init bsp_end_local_APIC_setup(void)
 }
 
 #ifdef CONFIG_X86_X2APIC
+/*
+ * Need to disable xapic and x2apic at the same time and then enable xapic mode
+ */
+static inline void __disable_x2apic(u64 msr)
+{
+       wrmsrl(MSR_IA32_APICBASE,
+              msr & ~(X2APIC_ENABLE | XAPIC_ENABLE));
+       wrmsrl(MSR_IA32_APICBASE, msr & ~X2APIC_ENABLE);
+}
+
+static void disable_x2apic(void)
+{
+       u64 msr;
+
+       if (!cpu_has_x2apic)
+               return;
+
+       rdmsrl(MSR_IA32_APICBASE, msr);
+       if (msr & X2APIC_ENABLE) {
+               u32 x2apic_id = read_apic_id();
+
+               if (x2apic_id >= 255)
+                       panic("Cannot disable x2apic, id: %08x\n", x2apic_id);
+
+               pr_info("Disabling x2apic\n");
+               __disable_x2apic(msr);
+
+               x2apic_disabled = 1;
+               x2apic_mode = 0;
+
+               register_lapic_address(mp_lapic_addr);
+       }
+}
+
 void check_x2apic(void)
 {
        if (x2apic_enabled()) {
@@ -1442,15 +1477,20 @@ void check_x2apic(void)
 
 void enable_x2apic(void)
 {
-       int msr, msr2;
+       u64 msr;
+
+       rdmsrl(MSR_IA32_APICBASE, msr);
+       if (x2apic_disabled) {
+               __disable_x2apic(msr);
+               return;
+       }
 
        if (!x2apic_mode)
                return;
 
-       rdmsr(MSR_IA32_APICBASE, msr, msr2);
        if (!(msr & X2APIC_ENABLE)) {
                printk_once(KERN_INFO "Enabling x2apic\n");
-               wrmsr(MSR_IA32_APICBASE, msr | X2APIC_ENABLE, msr2);
+               wrmsrl(MSR_IA32_APICBASE, msr | X2APIC_ENABLE);
        }
 }
 #endif /* CONFIG_X86_X2APIC */
@@ -1487,7 +1527,7 @@ void __init enable_IR_x2apic(void)
        ret = save_ioapic_entries();
        if (ret) {
                pr_info("Saving IO-APIC state failed: %d\n", ret);
-               goto out;
+               return;
        }
 
        local_irq_save(flags);
@@ -1499,13 +1539,19 @@ void __init enable_IR_x2apic(void)
        else
                ret = enable_IR();
 
+       if (!x2apic_supported())
+               goto nox2apic;
+
        if (ret < 0) {
                /* IR is required if there is APIC ID > 255 even when running
                 * under KVM
                 */
                if (max_physical_apicid > 255 ||
-                   !hypervisor_x2apic_available())
+                   !hypervisor_x2apic_available()) {
+                       if (x2apic_preenabled)
+                               disable_x2apic();
                        goto nox2apic;
+               }
                /*
                 * without IR all CPUs can be addressed by IOAPIC/MSI
                 * only in physical mode
@@ -1513,8 +1559,10 @@ void __init enable_IR_x2apic(void)
                x2apic_force_phys();
        }
 
-       if (ret == IRQ_REMAP_XAPIC_MODE)
+       if (ret == IRQ_REMAP_XAPIC_MODE) {
+               pr_info("x2apic not enabled, IRQ remapping is in xapic mode\n");
                goto nox2apic;
+       }
 
        x2apic_enabled = 1;
 
@@ -1529,17 +1577,6 @@ nox2apic:
                restore_ioapic_entries();
        legacy_pic->restore_mask();
        local_irq_restore(flags);
-
-out:
-       if (x2apic_enabled || !x2apic_supported())
-               return;
-
-       if (x2apic_preenabled)
-               panic("x2apic: enabled by BIOS but kernel init failed.");
-       else if (ret == IRQ_REMAP_XAPIC_MODE)
-               pr_info("x2apic not enabled, IRQ remapping is in xapic mode\n");
-       else if (ret < 0)
-               pr_info("x2apic not enabled, IRQ remapping init failed\n");
 }
 
 #ifdef CONFIG_X86_64

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 6d939d7847e293901538cfe32ae1b95d1d82551a..45b461fdb34490c7e3fdeac666475df2ed7a17e0 100644 (file)
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2948,6 +2948,10 @@ static inline void __init check_timer(void)
        }
        local_irq_disable();
        apic_printk(APIC_QUIET, KERN_INFO "..... failed :(.\n");
+       if (x2apic_preenabled)
+               apic_printk(APIC_QUIET, KERN_INFO
+                           "Perhaps problem with the pre-enabled x2apic mode\n"
+                           "Try booting with x2apic and interrupt-remapping disabled in the bios.\n");
        panic("IO-APIC + timer doesn't work!  Boot with apic=debug and send a "
                "report.  Then try booting with the 'noapic' option.\n");
 out: