KVM: x86: Defer the MMU unload to the normal path on an global INVPCID

Defer unloading the MMU after a INVPCID until the instruction emulation
has completed, i.e. until after RIP has been updated.

On VMX, this is a benign bug as VMX doesn't touch the MMU when skipping
an emulated instruction.  However, on SVM, if nrip is disabled, the
emulator is used to skip an instruction, which would lead to fireworks
if the emulator were invoked without a valid MMU.

Fixes: eb4b248 ("kvm: vmx: Support INVPCID in shadow paging mode")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305011101.3597423-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -11504,7 +11504,7 @@ int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva)
 
 		fallthrough;
 	case INVPCID_TYPE_ALL_INCL_GLOBAL:
-		kvm_mmu_unload(vcpu);
+		kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
 		return kvm_skip_emulated_instruction(vcpu);
 
 	default: