On 17.03.2009, at 13:04, Avi Kivity <avi@xxxxxxxxxx> wrote:
Alexander Graf wrote:
X86 CPUs need to have some magic happening to enable the
virtualization
extensions on them. This magic can result in unpleasant results for
users, like blocking other VMMs from working (vmx) or using invalid
TLB
entries (svm).
Currently KVM activates virtualization when the respective kernel
module
is loaded. This blocks us from autoloading KVM modules without
breaking
other VMMs.
To circumvent this problem at least a bit, this patch introduces on
demand activation of virtualization. This means, that instead
virtualization is enabled on creation of the first virtual machine
and disabled on destruction of the last one.
So using this, KVM can be easily autoloaded, while keeping other
hypervisors usable.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 68b217e..7c40743 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -65,6 +65,8 @@ DEFINE_SPINLOCK(kvm_lock);
LIST_HEAD(vm_list);
static cpumask_var_t cpus_hardware_enabled;
+static int kvm_usage_count = 0;
+static DEFINE_SPINLOCK(kvm_usage_lock);
Please use kvm_lock for this.
Looks good. Will do :-).
@@ -2327,14 +2341,40 @@ static struct miscdevice kvm_dev = {
&kvm_chardev_ops,
};
-static void hardware_enable(void *junk)
+static void hardware_enable(void *_r)
{
int cpu = raw_smp_processor_id();
+ int r;
+
+ /* If enabling a previous CPU failed already, let's not
continue */
+ if (_r && *((int*)_r))
+ return;
if (cpumask_test_cpu(cpu, cpus_hardware_enabled))
return;
+ r = kvm_arch_hardware_enable(NULL);
+ if (_r)
+ *((int*)_r) = r;
Racy. If one cpu succeeds and another fails, the successful one
could overwrite the failing one's result.
While the race will never happen (start two VMMs simultaneously) it
will cause an endless stream of complaints. Let's use an atomic_t
incremented on each failure.
Oh, and it can be global since we're inside a lock, so some of the
changes to add a return value become unnecessary.
Right, that probably cleans up things a bit.
+static void hardware_disable_all(void)
+{
+ if (!kvm_usage_count)
+ return;
Can this happen?
It should not. Better make it a BUG(...)?
+
+ spin_lock(&kvm_usage_lock);
+ kvm_usage_count--;
+ if (!kvm_usage_count)
+ on_each_cpu(hardware_disable, NULL, 1);
+ spin_unlock(&kvm_usage_lock);
+}
+
Please make sure cpu hotplug/hotunplug (and this suspend/resume)
still work.
Make sure as in test?
Alex
--
error compiling committee.c: too
many arguments to function
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