KVM: MMU: Move kvm_mmu_free_some_pages() into kvm_mmu_alloc_page()

What this function is doing is to ensure that the number of shadow pages
does not exceed the maximum limit stored in n_max_mmu_pages: so this is
placed at every code path that can reach kvm_mmu_alloc_page().

Although it might have some sense to spread this function in each such
code path when it could be called before taking mmu_lock, the rule was
changed not to do so.

Taking this background into account, this patch moves it into
kvm_mmu_alloc_page() and simplifies the code.

Note: the unlikely hint in kvm_mmu_free_some_pages() guarantees that the
overhead of this function is almost zero except when we actually need to
allocate some shadow pages, so we do not need to care about calling it
multiple times in one path by doing kvm_mmu_get_page() a few times.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -1505,6 +1505,9 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
 					       u64 *parent_pte, int direct)
 {
 	struct kvm_mmu_page *sp;
+
+	kvm_mmu_free_some_pages(vcpu);
+
 	sp = mmu_memory_cache_alloc(&vcpu->arch.mmu_page_header_cache);
 	sp->spt = mmu_memory_cache_alloc(&vcpu->arch.mmu_page_cache);
 	if (!direct)
@@ -2842,7 +2845,6 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, u32 error_code,
 	spin_lock(&vcpu->kvm->mmu_lock);
 	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
-	kvm_mmu_free_some_pages(vcpu);
 	if (likely(!force_pt_level))
 		transparent_hugepage_adjust(vcpu, &gfn, &pfn, &level);
 	r = __direct_map(vcpu, v, write, map_writable, level, gfn, pfn,
@@ -2920,7 +2922,6 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 
 	if (vcpu->arch.mmu.shadow_root_level == PT64_ROOT_LEVEL) {
 		spin_lock(&vcpu->kvm->mmu_lock);
-		kvm_mmu_free_some_pages(vcpu);
 		sp = kvm_mmu_get_page(vcpu, 0, 0, PT64_ROOT_LEVEL,
 				      1, ACC_ALL, NULL);
 		++sp->root_count;
@@ -2932,7 +2933,6 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 
 			ASSERT(!VALID_PAGE(root));
 			spin_lock(&vcpu->kvm->mmu_lock);
-			kvm_mmu_free_some_pages(vcpu);
 			sp = kvm_mmu_get_page(vcpu, i << (30 - PAGE_SHIFT),
 					      i << 30,
 					      PT32_ROOT_LEVEL, 1, ACC_ALL,
@@ -2971,7 +2971,6 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 		ASSERT(!VALID_PAGE(root));
 
 		spin_lock(&vcpu->kvm->mmu_lock);
-		kvm_mmu_free_some_pages(vcpu);
 		sp = kvm_mmu_get_page(vcpu, root_gfn, 0, PT64_ROOT_LEVEL,
 				      0, ACC_ALL, NULL);
 		root = __pa(sp->spt);
@@ -3005,7 +3004,6 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 				return 1;
 		}
 		spin_lock(&vcpu->kvm->mmu_lock);
-		kvm_mmu_free_some_pages(vcpu);
 		sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
 				      PT32_ROOT_LEVEL, 0,
 				      ACC_ALL, NULL);
@@ -3311,7 +3309,6 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 	spin_lock(&vcpu->kvm->mmu_lock);
 	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
-	kvm_mmu_free_some_pages(vcpu);
 	if (likely(!force_pt_level))
 		transparent_hugepage_adjust(vcpu, &gfn, &pfn, &level);
 	r = __direct_map(vcpu, gpa, write, map_writable,

arch/x86/kvm/paging_tmpl.h

@@ -627,7 +627,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 		goto out_unlock;
 
 	kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
-	kvm_mmu_free_some_pages(vcpu);
 	if (!force_pt_level)
 		transparent_hugepage_adjust(vcpu, &walker.gfn, &pfn, &level);
 	r = FNAME(fetch)(vcpu, addr, &walker, write_fault,