KVM: x86/mmu: Skip filling the gfn cache for guaranteed direct MMU topups

Don't bother filling the gfn array cache when the caller is a fully
direct MMU, i.e. won't need a gfn array for shadow pages.
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200703023545.8771-13-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -1102,7 +1102,7 @@ static void mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc)
 	}
 }
 
-static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
+static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 {
 	int r;
 
@@ -1115,10 +1115,12 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
 				   PT64_ROOT_MAX_LEVEL);
 	if (r)
 		return r;
+	if (maybe_indirect) {
 		r = mmu_topup_memory_cache(&vcpu->arch.mmu_gfn_array_cache,
 					   PT64_ROOT_MAX_LEVEL);
 		if (r)
 			return r;
+	}
 	return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache,
 				      PT64_ROOT_MAX_LEVEL);
 }
@@ -4132,7 +4134,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	if (fast_page_fault(vcpu, gpa, error_code))
 		return RET_PF_RETRY;
 
-	r = mmu_topup_memory_caches(vcpu);
+	r = mmu_topup_memory_caches(vcpu, false);
 	if (r)
 		return r;
 
@@ -5168,7 +5170,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
 {
 	int r;
 
-	r = mmu_topup_memory_caches(vcpu);
+	r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->direct_map);
 	if (r)
 		goto out;
 	r = mmu_alloc_roots(vcpu);
@@ -5362,7 +5364,7 @@ static void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	 * or not since pte prefetch is skiped if it does not have
 	 * enough objects in the cache.
 	 */
-	mmu_topup_memory_caches(vcpu);
+	mmu_topup_memory_caches(vcpu, true);
 
 	spin_lock(&vcpu->kvm->mmu_lock);
 

arch/x86/kvm/mmu/paging_tmpl.h

@@ -816,7 +816,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 		return RET_PF_EMULATE;
 	}
 
-	r = mmu_topup_memory_caches(vcpu);
+	r = mmu_topup_memory_caches(vcpu, true);
 	if (r)
 		return r;
 
@@ -904,7 +904,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
 	 * No need to check return value here, rmap_can_add() can
 	 * help us to skip pte prefetch later.
 	 */
-	mmu_topup_memory_caches(vcpu);
+	mmu_topup_memory_caches(vcpu, true);
 
 	if (!VALID_PAGE(root_hpa)) {
 		WARN_ON(1);