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Add a tunable to disable migration of MSI-X interrupts.

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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.

Submitted by:	Jeremiah Lott <jlott@averesystems.com> (original patch)
Approved by:	re (marius)
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D6947
This commit is contained in:
John Baldwin 2016-06-24 22:49:32 +00:00
parent 39ba705baf
commit be0319fd19
1 changed files with 14 additions and 0 deletions
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14
sys/x86/x86/msi.c
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@ -46,6 +46,7 @@ __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>
@ -148,6 +149,16 @@ struct pic msi_pic = {
.pic_reprogram_pin = NULL,
};
/*
* 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;
@ -226,6 +237,9 @@ msi_assign_cpu(struct intsrc *isrc, u_int apic_id)
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;