MFC 302181,302635: Disable MSI-X migration on older Xen hypervisors.

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.

302635:
xen: automatically disable MSI-X interrupt migration

If the hypervisor version is smaller than 4.6.0. Xen commits 74fd00 and
70a3cb are required on the hypervisor side for this to be fixed, and those
are only included in 4.6.0, so stay on the safe side and disable MSI-X
interrupt migration on anything older than 4.6.0.

It should not cause major performance degradation unless a lot of MSI-X
interrupts are allocated.
This commit is contained in:
John Baldwin 2016-08-05 17:13:25 +00:00
parent 52d665c4ea
commit 64258f4644
Notes: svn2git 2020-12-20 02:59:44 +00:00
svn path=/stable/10/; revision=303776
4 changed files with 49 additions and 2 deletions

View File

@ -144,6 +144,8 @@ struct nmi_pcpu {
extern struct mtx icu_lock;
extern int elcr_found;
extern int msix_disable_migration;
#ifndef DEV_ATPIC
void atpic_reset(void);
#endif

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@ -141,6 +141,8 @@ struct trapframe;
extern struct mtx icu_lock;
extern int elcr_found;
extern int msix_disable_migration;
#ifndef DEV_ATPIC
void atpic_reset(void);
#endif

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@ -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 +135,20 @@ struct pic msi_pic = { msi_enable_source, msi_disable_source, msi_eoi_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. Values have the following meaning:
*
* -1: automatic detection by FreeBSD
* 0: enable migration
* 1: disable migration
*/
int msix_disable_migration = -1;
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 +227,9 @@ 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;
@ -284,6 +302,11 @@ msi_init(void)
return;
}
if (msix_disable_migration == -1) {
/* The default is to allow migration of MSI-X interrupts. */
msix_disable_migration = 0;
}
msi_enabled = 1;
intr_register_pic(&msi_pic);
mtx_init(&msi_lock, "msi", NULL, MTX_DEF);

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@ -385,9 +385,29 @@ xen_hvm_init_hypercall_stubs(void)
return (ENXIO);
if (hypercall_stubs == NULL) {
int major, minor;
do_cpuid(base + 1, regs);
printf("XEN: Hypervisor version %d.%d detected.\n",
regs[0] >> 16, regs[0] & 0xffff);
major = regs[0] >> 16;
minor = regs[0] & 0xffff;
printf("XEN: Hypervisor version %d.%d detected.\n", major,
minor);
if (((major < 4) || (major == 4 && minor <= 5)) &&
msix_disable_migration == -1) {
/*
* Xen hypervisors prior to 4.6.0 do not properly
* handle updates to enabled MSI-X table entries,
* so disable MSI-X interrupt migration in that
* case.
*/
if (bootverbose)
printf(
"Disabling MSI-X interrupt migration due to Xen hypervisor bug.\n"
"Set machdep.msix_disable_migration=0 to forcefully enable it.\n");
msix_disable_migration = 1;
}
}
/*