KVM: Add compat ioctl for KVM_SET_SIGNAL_MASK

KVM has an ioctl to define which signal mask should be used while running
inside VCPU_RUN. At least for big endian systems, this mask is different
on 32-bit and 64-bit systems (though the size is identical).

Add a compat wrapper that converts the mask to whatever the kernel accepts,
allowing 32-bit kvm user space to set signal masks.

This patch fixes qemu with --enable-io-thread on ppc64 hosts when running
32-bit user land.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/kernel/compat.c b/kernel/compat.c
index fc9eb093..18197ae 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -890,6 +890,7 @@
 	case 1: set->sig[0] = compat->sig[0] | (((long)compat->sig[1]) << 32 );
 	}
 }
+EXPORT_SYMBOL_GPL(sigset_from_compat);
 
 asmlinkage long
 compat_sys_rt_sigtimedwait (compat_sigset_t __user *uthese,