svn commit: r303777 - stable/9/sys/x86/x86

[John Baldwin]

Author: jhb
Date: Fri Aug  5 17:14:45 2016
New Revision: 303777
URL: https://svnweb.freebsd.org/changeset/base/303777

Log:
  MFC 302181: Add a tunable to disable migration of MSI-X interrupts.
  
  The new 'machdep.disable_msix_migration' tunable can be set to 1 to
  disable migration of MSI-X interrupts.
  
  Xen versions prior to 4.6.0 do not properly handle updates to MSI-X
  table entries after the initial write.  In particular, the operation
  to unmask a table entry after updating it during migration is not
  propagated to the "real" table for passthrough devices causing the
  interrupt to remain masked.  At least some systems in EC2 are
  affected by this bug when using SRIOV.  The tunable can be set in
  loader.conf as a workaround.

Modified:
  stable/9/sys/x86/x86/msi.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/x86/x86/msi.c
==============================================================================
--- stable/9/sys/x86/x86/msi.c	Fri Aug  5 17:13:25 2016	(r303776)
+++ stable/9/sys/x86/x86/msi.c	Fri Aug  5 17:14:45 2016	(r303777)
@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/sx.h>
+#include <sys/sysctl.h>
 #include <sys/systm.h>
 #include <x86/apicreg.h>
 #include <machine/cputypes.h>
@@ -134,6 +135,16 @@ struct pic msi_pic = { msi_enable_source
 		       msi_source_pending, NULL, NULL, msi_config_intr,
 		       msi_assign_cpu };
 
+/*
+ * Xen hypervisors prior to 4.6.0 do not properly handle updates to
+ * enabled MSI-X table entries.  Allow migration of MSI-X interrupts
+ * to be disabled via a tunable.
+ */
+static int msix_disable_migration = 0;
+SYSCTL_INT(_machdep, OID_AUTO, disable_msix_migration, CTLFLAG_RDTUN,
+    &msix_disable_migration, 0,
+    "Disable migration of MSI-X interrupts between CPUs");
+
 static int msi_enabled;
 static int msi_last_irq;
 static struct mtx msi_lock;
@@ -212,6 +223,9 @@ msi_assign_cpu(struct intsrc *isrc, u_in
 	if (msi->msi_first != msi)
 		return (EINVAL);
 
+	if (msix_disable_migration && msi->msi_msix)
+		return (EINVAL);
+
 	/* Store information to free existing irq. */
 	old_vector = msi->msi_vector;
 	old_id = msi->msi_cpu;