[Xen-devel] [PATCH v3 2/6] xen: add hypercall option to override and restore vcpu affinity

[Juergen Gross <jgross@xxxxxxxx>]

Some hardware (e.g. Dell studio 1555 laptops) require SMIs to be
called on physical cpu 0 only. Linux drivers like dcdbas or i8k try
to achieve this by pinning the running thread to cpu 0, but in Dom0
this is not enough: the vcpu must be pinned to physical cpu 0 via
Xen, too.

Add a stable hypercall option SCHEDOP_pin_override to the sched_op
hypercall to achieve this. It is taking a physical cpu number as
parameter. If pinning is possible (the calling domain has the
privilege to make the call and the cpu is available in the domain's
cpupool) the calling vcpu is pinned to the specified cpu. The old
cpu affinity is saved. To undo the override pinning a negative cpu
value is specified. This will restore the original cpu affinity of
the vcpu.

Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2: - limit operation to hardware domain as suggested by Jan Beulich
    - some style issues corrected as requested by Jan Beulich
    - use fixed width types in interface as requested by Jan Beulich
    - add compat layer checking as requested by Jan Beulich

V3: - adjust coding style as requested by Jan Beulich
    - rename pin_temp to pin_override as requested by Jan Beulich and
      suggested by David Vrabel
    - change return type of do_pin_temp() to int as requested by Jan Beulich
    - swap error checks in do_sched_op() as requested by Jan Beulich
    - adjust comment in xen/include/public/sched.h as requested by Jan Beulich
---
 xen/common/compat/schedule.c |  4 ++
 xen/common/schedule.c        | 93 +++++++++++++++++++++++++++++++++++++++++---
 xen/include/public/sched.h   | 17 ++++++++
 xen/include/xen/sched.h      |  1 +
 xen/include/xlat.lst         |  1 +
 5 files changed, 111 insertions(+), 5 deletions(-)

diff --git a/xen/common/compat/schedule.c b/xen/common/compat/schedule.c
index 812c550..8b6e6f1 100644
--- a/xen/common/compat/schedule.c
+++ b/xen/common/compat/schedule.c
@@ -10,6 +10,10 @@
 
 #define do_sched_op compat_sched_op
 
+#define xen_sched_pin_override sched_pin_override
+CHECK_sched_pin_override;
+#undef xen_sched_pin_override
+
 #define xen_sched_shutdown sched_shutdown
 CHECK_sched_shutdown;
 #undef xen_sched_shutdown
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 13803ec..e57b659 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -271,6 +271,12 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
     struct scheduler *old_ops;
     void *old_domdata;
 
+    for_each_vcpu ( d, v )
+    {
+        if ( v->affinity_broken )
+            return -EBUSY;
+    }
+
     domdata = SCHED_OP(c->sched, alloc_domdata, d);
     if ( domdata == NULL )
         return -ENOMEM;
@@ -669,6 +675,14 @@ int cpu_disable_scheduler(unsigned int cpu)
             if ( cpumask_empty(&online_affinity) &&
                  cpumask_test_cpu(cpu, v->cpu_hard_affinity) )
             {
+                if ( v->affinity_broken )
+                {
+                    /* The vcpu is temporarily pinned, can't move it. */
+                    vcpu_schedule_unlock_irqrestore(lock, flags, v);
+                    ret = -EBUSY;
+                    break;
+                }
+
                 if (system_state == SYS_STATE_suspend)
                 {
                     cpumask_copy(v->cpu_hard_affinity_saved,
@@ -752,14 +766,22 @@ static int vcpu_set_affinity(
     struct vcpu *v, const cpumask_t *affinity, cpumask_t *which)
 {
     spinlock_t *lock;
+    int ret = 0;
 
     lock = vcpu_schedule_lock_irq(v);
 
-    cpumask_copy(which, affinity);
+    if ( v->affinity_broken )
+        ret = -EBUSY;
+    else
+    {
+        cpumask_copy(which, affinity);
 
-    /* Always ask the scheduler to re-evaluate placement
-     * when changing the affinity */
-    set_bit(_VPF_migrating, &v->pause_flags);
+        /*
+         * Always ask the scheduler to re-evaluate placement
+         * when changing the affinity.
+         */
+        set_bit(_VPF_migrating, &v->pause_flags);
+    }
 
     vcpu_schedule_unlock_irq(lock, v);
 
@@ -771,7 +793,7 @@ static int vcpu_set_affinity(
         vcpu_migrate(v);
     }
 
-    return 0;
+    return ret;
 }
 
 int vcpu_set_hard_affinity(struct vcpu *v, const cpumask_t *affinity)
@@ -982,6 +1004,50 @@ void watchdog_domain_destroy(struct domain *d)
         kill_timer(&d->watchdog_timer[i]);
 }
 
+int vcpu_pin_override(struct vcpu *v, int cpu)
+{
+    spinlock_t *lock;
+    int ret = -EINVAL;
+
+    lock = vcpu_schedule_lock_irq(v);
+
+    if ( cpu < 0 )
+    {
+        if ( v->affinity_broken )
+        {
+            cpumask_copy(v->cpu_hard_affinity, v->cpu_hard_affinity_saved);
+            v->affinity_broken = 0;
+            set_bit(_VPF_migrating, &v->pause_flags);
+            ret = 0;
+        }
+    }
+    else if ( cpu < nr_cpu_ids )
+    {
+        if ( v->affinity_broken )
+            ret = -EBUSY;
+        else if ( cpumask_test_cpu(cpu, VCPU2ONLINE(v)) )
+        {
+            cpumask_copy(v->cpu_hard_affinity_saved, v->cpu_hard_affinity);
+            v->affinity_broken = 1;
+            cpumask_copy(v->cpu_hard_affinity, cpumask_of(cpu));
+            set_bit(_VPF_migrating, &v->pause_flags);
+            ret = 0;
+        }
+    }
+
+    vcpu_schedule_unlock_irq(lock, v);
+
+    domain_update_node_affinity(v->domain);
+
+    if ( v->pause_flags & VPF_migrating )
+    {
+        vcpu_sleep_nosync(v);
+        vcpu_migrate(v);
+    }
+
+    return ret;
+}
+
 typedef long ret_t;
 
 #endif /* !COMPAT */
@@ -1091,6 +1157,23 @@ ret_t do_sched_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
arg)
         break;
     }
 
+    case SCHEDOP_pin_override:
+    {
+        struct sched_pin_override sched_pin_override;
+
+        ret = -EPERM;
+        if ( !is_hardware_domain(current->domain) )
+            break;
+
+        ret = -EFAULT;
+        if ( copy_from_guest(&sched_pin_override, arg, 1) )
+            break;
+
+        ret = vcpu_pin_override(current, sched_pin_override.pcpu);
+
+        break;
+    }
+
     default:
         ret = -ENOSYS;
     }
diff --git a/xen/include/public/sched.h b/xen/include/public/sched.h
index 2219696..82c338f 100644
--- a/xen/include/public/sched.h
+++ b/xen/include/public/sched.h
@@ -118,6 +118,17 @@
  * With id != 0 and timeout != 0, poke watchdog timer and set new timeout.
  */
 #define SCHEDOP_watchdog    6
+
+/*
+ * Override the current vcpu affinity by pinning it to one physical cpu or undo
+ * this override restoring the previous affinity.
+ * @arg == pointer to sched_pin_override_t structure.
+ *
+ * A negative pcpu value will undo a previous pin override and restore the
+ * previous cpu affinity.
+ * This call is allowed for the hardware domain only.
+ */
+#define SCHEDOP_pin_override 7
 /* ` } */
 
 struct sched_shutdown {
@@ -148,6 +159,12 @@ struct sched_watchdog {
 typedef struct sched_watchdog sched_watchdog_t;
 DEFINE_XEN_GUEST_HANDLE(sched_watchdog_t);
 
+struct sched_pin_override {
+    int32_t pcpu;
+};
+typedef struct sched_pin_override sched_pin_override_t;
+DEFINE_XEN_GUEST_HANDLE(sched_pin_override_t);
+
 /*
  * Reason codes for SCHEDOP_shutdown. These may be interpreted by control
  * software to determine the appropriate action. For the most part, Xen does
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index cc77d70..09fff5f 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -811,6 +811,7 @@ int cpu_disable_scheduler(unsigned int cpu);
 int vcpu_set_hard_affinity(struct vcpu *v, const cpumask_t *affinity);
 int vcpu_set_soft_affinity(struct vcpu *v, const cpumask_t *affinity);
 void restore_vcpu_affinity(struct domain *d);
+int vcpu_pin_override(struct vcpu *v, int cpu);
 
 void vcpu_runstate_get(struct vcpu *v, struct vcpu_runstate_info *runstate);
 uint64_t get_cpu_idle_time(unsigned int cpu);
diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
index fda1137..23befb3 100644
--- a/xen/include/xlat.lst
+++ b/xen/include/xlat.lst
@@ -104,6 +104,7 @@
 ?      pmu_data                        pmu.h
 ?      pmu_params                      pmu.h
 !      sched_poll                      sched.h
+?      sched_pin_override              sched.h
 ?      sched_remote_shutdown           sched.h
 ?      sched_shutdown                  sched.h
 ?      tmem_oid                        tmem.h
-- 
2.6.2


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