x86, x2apic: Enable the bios request for x2apic optout

On the platforms which are x2apic and interrupt-remapping
capable, Linux kernel is enabling x2apic even if the BIOS
doesn't. This is to take advantage of the features that x2apic
brings in.

Some of the OEM platforms are running into issues because of
this, as their bios is not x2apic aware. For example, this was
resulting in interrupt migration issues on one of the platforms.
Also if the BIOS SMI handling uses APIC interface to send SMI's,
then the BIOS need to be aware of x2apic mode that OS has
enabled.

On some of these platforms, BIOS doesn't have a HW mechanism to
turnoff the x2apic feature to prevent OS from enabling it.

To resolve this mess, recent changes to the VT-d2 specification:

 http://download.intel.com/technology/computing/vptech/Intel(r)_VT_for_Direct_IO.pdf

includes a mechanism that provides BIOS a way to request system
software to opt out of enabling x2apic mode.

Look at the x2apic optout flag in the DMAR tables before
enabling the x2apic mode in the platform. Also print a warning
that we have disabled x2apic based on the BIOS request.

Kernel boot parameter "intremap=no_x2apic_optout" can be used to
override the BIOS x2apic optout request.

Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: yinghai@kernel.org
Cc: joerg.roedel@amd.com
Cc: tony.luck@intel.com
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/20110824001456.171766616@sbsiddha-desk.sc.intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 16 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 52fa56399a50..6b9874a5c7af 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1440,24 +1440,18 @@ int __init enable_IR(void)
 #ifdef CONFIG_INTR_REMAP
         if (!intr_remapping_supported()) {
                 pr_debug("intr-remapping not supported\n");
-                return 0;
+                return -1;
         }
 
         if (!x2apic_preenabled && skip_ioapic_setup) {
                 pr_info("Skipped enabling intr-remap because of skipping "
                         "io-apic setup\n");
-                return 0;
+                return -1;
         }
 
-        if (enable_intr_remapping(x2apic_supported()))
-                return 0;
-
-        pr_info("Enabled Interrupt-remapping\n");
-
-        return 1;
-
+        return enable_intr_remapping();
 #endif
-        return 0;
+        return -1;
 }
 
 void __init enable_IR_x2apic(void)
@@ -1481,11 +1475,11 @@ void __init enable_IR_x2apic(void)
         mask_ioapic_entries();
 
         if (dmar_table_init_ret)
-                ret = 0;
+                ret = -1;
         else
                 ret = enable_IR();
 
-        if (!ret) {
+        if (ret < 0) {
                 /* IR is required if there is APIC ID > 255 even when running
                  * under KVM
                  */
@@ -1499,6 +1493,9 @@ void __init enable_IR_x2apic(void)
                 x2apic_force_phys();
         }
 
+        if (ret == IRQ_REMAP_XAPIC_MODE)
+                goto nox2apic;
+
         x2apic_enabled = 1;
 
         if (x2apic_supported() && !x2apic_mode) {
@@ -1508,19 +1505,21 @@ void __init enable_IR_x2apic(void)
         }
 
 nox2apic:
-        if (!ret) /* IR enabling failed */
+        if (ret < 0) /* IR enabling failed */
                 restore_ioapic_entries();
         legacy_pic->restore_mask();
         local_irq_restore(flags);
 
 out:
-        if (x2apic_enabled)
+        if (x2apic_enabled || !x2apic_supported())
                 return;
 
         if (x2apic_preenabled)
                 panic("x2apic: enabled by BIOS but kernel init failed.");
-        else if (cpu_has_x2apic)
-                pr_info("Not enabling x2apic, Intr-remapping init failed.\n");
+        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