KVM: Activate Virtualization On Demand

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.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 73cb5dd960cf..a187570e4837 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1138,12 +1138,15 @@ static __init int vmx_disabled_by_bios(void)
         /* locked but not enabled */
 }
 
-static void hardware_enable(void *garbage)
+static int hardware_enable(void *garbage)
 {
         int cpu = raw_smp_processor_id();
         u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
         u64 old;
 
+        if (read_cr4() & X86_CR4_VMXE)
+                return -EBUSY;
+
         INIT_LIST_HEAD(&per_cpu(vcpus_on_cpu, cpu));
         rdmsrl(MSR_IA32_FEATURE_CONTROL, old);
         if ((old & (FEATURE_CONTROL_LOCKED |
@@ -1158,6 +1161,10 @@ static void hardware_enable(void *garbage)
         asm volatile (ASM_VMX_VMXON_RAX
                       : : "a"(&phys_addr), "m"(phys_addr)
                       : "memory", "cc");
+
+        ept_sync_global();
+
+        return 0;
 }
 
 static void vmclear_local_vcpus(void)
@@ -4040,8 +4047,6 @@ static int __init vmx_init(void)
         if (bypass_guest_pf)
                 kvm_mmu_set_nonpresent_ptes(~0xffeull, 0ull);
 
-        ept_sync_global();
-
         return 0;
 
 out3: