[Xen-devel] [PATCH V2] keep iommu disabled until iommu_setup() is called

[Ronny Hegewald <ronny.hegewald@xxxxxxxxx>]

The iommu is enabled by default when xen is booting and later disabled in 
iommu_setup() when no iommu is present.

But under some circumstances iommu-code can be called before iommu_setup() is 
processed. If there is no iommu available xen crashes.

This can happen for example when panic(...) is called that got introduced with
patch "x86-64: detect processors subject to AMD erratum #121 and refuse to 
boot." since xen 4.1.3 and results in the following stacktrace:

   find_iommu_for_device
   amd_iommu_ioapic_update_ire
   timer_interrupt
   enable_8259_A_irq
   do_IRQ
   printk_start_of_line
   acpi_os_printf
   io_apic_write
   __ioapic_write_entry
   ioapic_write_entry
   __clear_IO_APIC_pin
   clear_IO_APIC
   disable_IO_APIC
   __stop_this_cpu
   smp_send_stop
   machine_restart
   panic
   tasklet_schedule_on_cpu
   display_cacheinfo
   init_amd
   generic_identify
   identify_cpu
   _start_xen
   _high_start


This patch fixes this by keeping the iommu disabled until iommu_setup() is 
entered. 

Signed-off-by: Ronny Hegewald@xxxxxxxxx

---
Changed since V1:
   * simplify code as suggested by Jan Beulich

--- xen/drivers/passthrough/iommu.c.org 2012-10-05 03:38:33.000000000 +0000
+++ xen/drivers/passthrough/iommu.c     2012-10-21 21:07:37.000000000 +0000
@@ -38,7 +38,8 @@
  *   no-intremap                Disable VT-d Interrupt Remapping
  */
 custom_param("iommu", parse_iommu_param);
-bool_t __read_mostly iommu_enabled = 1;
+bool_t iommu_enable_default __initdata = 1;
+bool_t __read_mostly iommu_enabled;
 bool_t __read_mostly force_iommu;
 bool_t __initdata iommu_dom0_strict;
 bool_t __read_mostly iommu_verbose;
@@ -61,7 +62,7 @@
             *ss = '\0';
 
         if ( !parse_bool(s) )
-            iommu_enabled = 0;
+            iommu_enable_default = 0;
         else if ( !strcmp(s, "force") || !strcmp(s, "required") )
             force_iommu = 1;
         else if ( !strcmp(s, "workaround_bios_bug") )
@@ -316,7 +317,7 @@
     if ( iommu_dom0_strict )
         iommu_passthrough = 0;
 
-    if ( iommu_enabled )
+    if ( iommu_enable_default )
     {
         rc = iommu_hardware_setup();
         iommu_enabled = (rc == 0);




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel