KVM: halt_polling: improve grow/shrink settings

Right now halt_poll_ns can be change during runtime. The
grow and shrink factors can only be set during module load.
Lets fix several aspects of grow shrink:
- make grow/shrink changeable by root
- make all variables unsigned int
- read the variables once to prevent races

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
index d6f83222a6a1671ec819d730801398ebb88f80ab..aa69253ecc7dd94df775361ac6c6f5b70c6e0dfc 100644 (file)
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -359,14 +359,15 @@ TRACE_EVENT(
 #endif
 
 TRACE_EVENT(kvm_halt_poll_ns,
-       TP_PROTO(bool grow, unsigned int vcpu_id, int new, int old),
+       TP_PROTO(bool grow, unsigned int vcpu_id, unsigned int new,
+                unsigned int old),
        TP_ARGS(grow, vcpu_id, new, old),
 
        TP_STRUCT__entry(
                __field(bool, grow)
                __field(unsigned int, vcpu_id)
-               __field(int, new)
-               __field(int, old)
+               __field(unsigned int, new)
+               __field(unsigned int, old)
        ),
 
        TP_fast_assign(
@@ -376,7 +377,7 @@ TRACE_EVENT(kvm_halt_poll_ns,
                __entry->old            = old;
        ),
 
-       TP_printk("vcpu %u: halt_poll_ns %d (%s %d)",
+       TP_printk("vcpu %u: halt_poll_ns %u (%s %u)",
                        __entry->vcpu_id,
                        __entry->new,
                        __entry->grow ? "grow" : "shrink",

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a11cfd20a6a0d2aa86b1d06b8552bc41a8bfd8c9..ba45e41c321040bd947f52c3df792a7f422b04bd 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -72,11 +72,11 @@ module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
 
 /* Default doubles per-vcpu halt_poll_ns. */
 static unsigned int halt_poll_ns_grow = 2;
-module_param(halt_poll_ns_grow, int, S_IRUGO);
+module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR);
 
 /* Default resets per-vcpu halt_poll_ns . */
 static unsigned int halt_poll_ns_shrink;
-module_param(halt_poll_ns_shrink, int, S_IRUGO);
+module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR);
 
 /*
  * Ordering of locks:
@@ -1943,14 +1943,15 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
 static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-       int old, val;
+       unsigned int old, val, grow;
 
        old = val = vcpu->halt_poll_ns;
+       grow = READ_ONCE(halt_poll_ns_grow);
        /* 10us base */
-       if (val == 0 && halt_poll_ns_grow)
+       if (val == 0 && grow)
                val = 10000;
        else
-               val *= halt_poll_ns_grow;
+               val *= grow;
 
        vcpu->halt_poll_ns = val;
        trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
@@ -1958,13 +1959,14 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 
 static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-       int old, val;
+       unsigned int old, val, shrink;
 
        old = val = vcpu->halt_poll_ns;
-       if (halt_poll_ns_shrink == 0)
+       shrink = READ_ONCE(halt_poll_ns_shrink);
+       if (shrink == 0)
                val = 0;
        else
-               val /= halt_poll_ns_shrink;
+               val /= shrink;
 
        vcpu->halt_poll_ns = val;
        trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old);