On 05.11.2008, at 21:58, Eduardo Habkost wrote:
On Wed, Nov 05, 2008 at 11:41:04AM +0100, 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 removal of the last one.
So using this, KVM can be easily autoloaded, while keeping other
hypervisors usable.
v2 adds returns to non-x86 hardware_enables and adds IA64 change
v3 changes:
- use spin_lock instead of atomics
- put locking to new functions hardware_{en,dis}able_all that get
called
on VM creation/destruction
- remove usage counter checks where not necessary
- return -EINVAL for IA64 slot < 0 case
Signed-off-by: Alexander Graf <[EMAIL PROTECTED]>
---
<snip>
-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 (cpu_isset(cpu, cpus_hardware_enabled))
return;
+ r = kvm_arch_hardware_enable(NULL);
+ if (_r)
+ *((int*)_r) = r;
+ if (r) {
+ printk(KERN_INFO "kvm: enabling virtualization on "
+ "CPU%d failed\n", cpu);
+ return;
+ }
+
cpu_set(cpu, cpus_hardware_enabled);
- kvm_arch_hardware_enable(NULL);
+}
Doesn't on_each_cpu() run the function in parallel on all CPUs? If so,
there is a race between checking *_r and setting *_r.
Good question - it doesn't really hurt to write the value though, if
we only write it on error.
So I guess we could just remove the first check and check on if( r &&
_r) later on.
Alex
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