6062 Workaround broken KVM handling of directed EOIs
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>

*** 22,31 ****
--- 22,32 ----
   * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  /*
   * Copyright 2014 Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
+  * Copyright (c) 2014 by Delphix. All rights reserved.
   */
  
  #include <sys/cpuvar.h>
  #include <sys/psm.h>
  #include <sys/archsystm.h>
*** 64,73 ****
--- 65,77 ----
   * -----------------------------------------------------------
   */
  int     x2apic_enable = 1;
  apic_mode_t apic_mode = LOCAL_APIC;     /* Default mode is Local APIC */
  
+ /* See apic_directed_EOI_supported().  Currently 3-state variable. */
+ volatile int apic_directed_eoi_state = 2;
+ 
  /* Uses MMIO (Memory Mapped IO) */
  static apic_reg_ops_t local_apic_regs_ops = {
          local_apic_read,
          local_apic_write,
          get_local_apic_pri,
*** 292,301 ****
--- 296,340 ----
  int
  apic_directed_EOI_supported()
  {
          uint32_t ver;
  
+         /*
+          * There are some known issues with some versions of Linux KVM and QEMU
+          * where by directed EOIs do not properly function and instead get
+          * coalesced at the hypervisor, causing the host not to see interrupts.
+          * Thus, when the platform is KVM, we would like to disable it by
+          * default, but keep it available otherwise.
+          *
+          * We use a three-state variable (apic_directed_eoi_state) to determine
+          * how we handle directed EOI.
+          *
+          * 0 --> Don't do directed EOI at all.
+          * 1 --> Do directed EOI if available, no matter the HW environment.
+          * 2 --> Don't do directed EOI on KVM, but do it otherwise if available.
+          *
+          * If some grinning weirdo put something else in there, treat it as '2'
+          * (i.e. the current default).
+          *
+          * Note, at this time illumos KVM does not identify as KVM. If it does,
+          * we'll need to do some work to determine if it should be caught by
+          * this or if it should show up as its own value of platform_type.
+          */
+         switch (apic_directed_eoi_state) {
+         case 0:
+                 /* Don't do it at all. */
+                 return (0);
+         case 1:
+                 break;
+         case 2:
+         default:
+                 /* Only do it if we aren't on KVM. */
+                 if (get_hwenv() == HW_KVM)
+                         return (0);
+                 /* FALLTHRU */
+         }
+ 
          ver = apic_reg_ops->apic_read(APIC_VERS_REG);
          if (ver & APIC_DIRECTED_EOI_BIT)
                  return (1);
  
          return (0);