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, 36 insertions, 8 deletions

diff --git a/drivers/iommu/intr_remapping.c b/drivers/iommu/intr_remapping.c
index 1a89d4a2cadf..51a2ce9b8789 100644
--- a/drivers/iommu/intr_remapping.c
+++ b/drivers/iommu/intr_remapping.c
@@ -21,6 +21,7 @@ int intr_remapping_enabled;
 
 static int disable_intremap;
 static int disable_sourceid_checking;
+static int no_x2apic_optout;
 
 static __init int setup_nointremap(char *str)
 {
@@ -34,12 +35,20 @@ static __init int setup_intremap(char *str)
         if (!str)
                 return -EINVAL;
 
-        if (!strncmp(str, "on", 2))
-                disable_intremap = 0;
-        else if (!strncmp(str, "off", 3))
-                disable_intremap = 1;
-        else if (!strncmp(str, "nosid", 5))
-                disable_sourceid_checking = 1;
+        while (*str) {
+                if (!strncmp(str, "on", 2))
+                        disable_intremap = 0;
+                else if (!strncmp(str, "off", 3))
+                        disable_intremap = 1;
+                else if (!strncmp(str, "nosid", 5))
+                        disable_sourceid_checking = 1;
+                else if (!strncmp(str, "no_x2apic_optout", 16))
+                        no_x2apic_optout = 1;
+
+                str += strcspn(str, ",");
+                while (*str == ',')
+                        str++;
+        }
 
         return 0;
 }
@@ -501,6 +510,15 @@ end:
         spin_unlock_irqrestore(&iommu->register_lock, flags);
 }
 
+static int __init dmar_x2apic_optout(void)
+{
+        struct acpi_table_dmar *dmar;
+        dmar = (struct acpi_table_dmar *)dmar_tbl;
+        if (!dmar || no_x2apic_optout)
+                return 0;
+        return dmar->flags & DMAR_X2APIC_OPT_OUT;
+}
+
 int __init intr_remapping_supported(void)
 {
         struct dmar_drhd_unit *drhd;
@@ -521,16 +539,25 @@ int __init intr_remapping_supported(void)
         return 1;
 }
 
-int __init enable_intr_remapping(int eim)
+int __init enable_intr_remapping(void)
 {
         struct dmar_drhd_unit *drhd;
         int setup = 0;
+        int eim = 0;
 
         if (parse_ioapics_under_ir() != 1) {
                 printk(KERN_INFO "Not enable interrupt remapping\n");
                 return -1;
         }
 
+        if (x2apic_supported()) {
+                eim = !dmar_x2apic_optout();
+                WARN(!eim, KERN_WARNING
+                           "Your BIOS is broken and requested that x2apic be disabled\n"
+                           "This will leave your machine vulnerable to irq-injection attacks\n"
+                           "Use 'intremap=no_x2apic_optout' to override BIOS request\n");
+        }
+
         for_each_drhd_unit(drhd) {
                 struct intel_iommu *iommu = drhd->iommu;
 
@@ -606,8 +633,9 @@ int __init enable_intr_remapping(int eim)
                 goto error;
 
         intr_remapping_enabled = 1;
+        pr_info("Enabled IRQ remapping in %s mode\n", eim ? "x2apic" : "xapic");
 
-        return 0;
+        return eim ? IRQ_REMAP_X2APIC_MODE : IRQ_REMAP_XAPIC_MODE;
 
 error:
         /*