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

@@ -22,10 +22,11 @@
  * 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>

@@ -64,10 +65,13 @@
  * -----------------------------------------------------------
  */
 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,

@@ -292,10 +296,45 @@
 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);