KVM: x86/mmu: Pivot on "TDP MMU enabled" to check if active MMU is TDP MMU

Simplify and optimize the logic for detecting if the current/active MMU
is a TDP MMU.  If the TDP MMU is globally enabled, then the active MMU is
a TDP MMU if it is direct.  When TDP is enabled, so called nonpaging MMUs
are never used as the only form of shadow paging KVM uses is for nested
TDP, and the active MMU can't be direct in that case.

Rename the helper and take the vCPU instead of an arbitrary MMU, as
nonpaging MMUs can show up in the walk_mmu if L1 is using nested TDP and
L2 has paging disabled.  Taking the vCPU has the added bonus of cleaning
up the callers, all of which check the current MMU but wrap code that
consumes the vCPU.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221012181702.3663607-9-seanjc@google.com>
[Use tdp_mmu_enabled variable. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -616,9 +616,14 @@ static bool mmu_spte_age(u64 *sptep)
 	return true;
 }
 
+static inline bool is_tdp_mmu_active(struct kvm_vcpu *vcpu)
+{
+	return tdp_mmu_enabled && vcpu->arch.mmu->root_role.direct;
+}
+
 static void walk_shadow_page_lockless_begin(struct kvm_vcpu *vcpu)
 {
-	if (is_tdp_mmu(vcpu->arch.mmu)) {
+	if (is_tdp_mmu_active(vcpu)) {
 		kvm_tdp_mmu_walk_lockless_begin();
 	} else {
 		/*
@@ -637,7 +642,7 @@ static void walk_shadow_page_lockless_begin(struct kvm_vcpu *vcpu)
 
 static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
 {
-	if (is_tdp_mmu(vcpu->arch.mmu)) {
+	if (is_tdp_mmu_active(vcpu)) {
 		kvm_tdp_mmu_walk_lockless_end();
 	} else {
 		/*
@@ -4043,7 +4048,7 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
 
 	walk_shadow_page_lockless_begin(vcpu);
 
-	if (is_tdp_mmu(vcpu->arch.mmu))
+	if (is_tdp_mmu_active(vcpu))
 		leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, &root);
 	else
 		leaf = get_walk(vcpu, addr, sptes, &root);

arch/x86/kvm/mmu/tdp_mmu.h

@@ -72,26 +72,8 @@ u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,
 
 #ifdef CONFIG_X86_64
 static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
-
-static inline bool is_tdp_mmu(struct kvm_mmu *mmu)
-{
-	struct kvm_mmu_page *sp;
-	hpa_t hpa = mmu->root.hpa;
-
-	if (WARN_ON(!VALID_PAGE(hpa)))
-		return false;
-
-	/*
-	 * A NULL shadow page is legal when shadowing a non-paging guest with
-	 * PAE paging, as the MMU will be direct with root_hpa pointing at the
-	 * pae_root page, not a shadow page.
-	 */
-	sp = to_shadow_page(hpa);
-	return sp && is_tdp_mmu_page(sp) && sp->root_count;
-}
 #else
 static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
-static inline bool is_tdp_mmu(struct kvm_mmu *mmu) { return false; }
 #endif
 
 #endif /* __KVM_X86_MMU_TDP_MMU_H */