KVM: x86: Handle SRCU initialization failure during page track init

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Handle SRCU initialization failure during page track init Check the return of init_srcu_struct(), which can fail due to OOM, when initializing the page track mechanism. Lack of checking leads to a NULL pointer deref found by a modified syzkaller. [Move the call towards the beginning of kvm_arch_init_vm. - Paolo]