KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid()

The KVM doesn't know whether any TLB for a specific pcid is cached in
the CPU when tdp is enabled.  So it is better to flush all the guest
TLB when invalidating any single PCID context.

The case is very rare or even impossible since KVM generally doesn't
intercept CR3 write or INVPCID instructions when tdp is enabled, so the
fix is mostly for the sake of overall robustness.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -1073,6 +1073,18 @@ static void kvm_invalidate_pcid(struct kvm_vcpu *vcpu, unsigned long pcid)
 	unsigned long roots_to_free = 0;
 	int i;
 
+	/*
+	 * MOV CR3 and INVPCID are usually not intercepted when using TDP, but
+	 * this is reachable when running EPT=1 and unrestricted_guest=0,  and
+	 * also via the emulator.  KVM's TDP page tables are not in the scope of
+	 * the invalidation, but the guest's TLB entries need to be flushed as
+	 * the CPU may have cached entries in its TLB for the target PCID.
+	 */
+	if (unlikely(tdp_enabled)) {
+		kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
+		return;
+	}
+
 	/*
 	 * If neither the current CR3 nor any of the prev_roots use the given
 	 * PCID, then nothing needs to be done here because a resync will