KVM: fx_init() needs preemption disabled while it plays with the FPU state

Now that kvm generally runs with preemption enabled, we need to protect
the fpu intialization sequence.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 7aeaaba79c54..5b42731beba4 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -693,10 +693,13 @@ void fx_init(struct kvm_vcpu *vcpu)
 
         } *fx_image;
 
+        /* Initialize guest FPU by resetting ours and saving into guest's */
+        preempt_disable();
         fx_save(vcpu->host_fx_image);
         fpu_init();
         fx_save(vcpu->guest_fx_image);
         fx_restore(vcpu->host_fx_image);
+        preempt_enable();
 
         fx_image = (struct fx_image_s *)vcpu->guest_fx_image;
         fx_image->mxcsr = 0x1f80;