kvm: x86/mmu: Support zapping SPTEs in the TDP MMU

Add functions to zap SPTEs to the TDP MMU. These are needed to tear down
TDP MMU roots properly and implement other MMU functions which require
tearing down mappings. Future patches will add functions to populate the
page tables, but as for this patch there will not be any work for these
functions to do.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538

Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20201014182700.2888246-8-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -5371,6 +5371,10 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
 	kvm_reload_remote_mmus(kvm);
 
 	kvm_zap_obsolete_pages(kvm);
+
+	if (kvm->arch.tdp_mmu_enabled)
+		kvm_tdp_mmu_zap_all(kvm);
+
 	spin_unlock(&kvm->mmu_lock);
 }
 
@@ -5411,6 +5415,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *memslot;
 	int i;
+	bool flush;
 
 	spin_lock(&kvm->mmu_lock);
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
@@ -5430,6 +5435,12 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 		}
 	}
 
+	if (kvm->arch.tdp_mmu_enabled) {
+		flush = kvm_tdp_mmu_zap_gfn_range(kvm, gfn_start, gfn_end);
+		if (flush)
+			kvm_flush_remote_tlbs(kvm);
+	}
+
 	spin_unlock(&kvm->mmu_lock);
 }
 
@@ -5596,6 +5607,10 @@ restart:
 	}
 
 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
+
+	if (kvm->arch.tdp_mmu_enabled)
+		kvm_tdp_mmu_zap_all(kvm);
+
 	spin_unlock(&kvm->mmu_lock);
 }
 

arch/x86/kvm/mmu/tdp_iter.c

@@ -175,3 +175,8 @@ void tdp_iter_refresh_walk(struct tdp_iter *iter)
 		       iter->root_level, iter->min_level, goal_gfn);
 }
 
+u64 *tdp_iter_root_pt(struct tdp_iter *iter)
+{
+	return iter->pt_path[iter->root_level - 1];
+}
+

arch/x86/kvm/mmu/tdp_iter.h

@@ -52,5 +52,6 @@ void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
 		    int min_level, gfn_t goal_gfn);
 void tdp_iter_next(struct tdp_iter *iter);
 void tdp_iter_refresh_walk(struct tdp_iter *iter);
+u64 *tdp_iter_root_pt(struct tdp_iter *iter);
 
 #endif /* __KVM_X86_MMU_TDP_ITER_H */

arch/x86/kvm/mmu/tdp_mmu.c

@@ -49,8 +49,13 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
 	return sp->tdp_mmu_page && sp->root_count;
 }
 
+static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
+			  gfn_t start, gfn_t end);
+
 void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
 {
+	gfn_t max_gfn = 1ULL << (boot_cpu_data.x86_phys_bits - PAGE_SHIFT);
+
 	lockdep_assert_held(&kvm->mmu_lock);
 
 	WARN_ON(root->root_count);
@@ -58,6 +63,8 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
 
 	list_del(&root->link);
 
+	zap_gfn_range(kvm, root, 0, max_gfn);
+
 	free_page((unsigned long)root->spt);
 	kmem_cache_free(mmu_page_header_cache, root);
 }
@@ -135,6 +142,11 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
 static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 				u64 old_spte, u64 new_spte, int level);
 
+static int kvm_mmu_page_as_id(struct kvm_mmu_page *sp)
+{
+	return sp->role.smm ? 1 : 0;
+}
+
 /**
  * handle_changed_spte - handle bookkeeping associated with an SPTE change
  * @kvm: kvm instance
@@ -242,3 +254,104 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 {
 	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level);
 }
+
+static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
+				    u64 new_spte)
+{
+	u64 *root_pt = tdp_iter_root_pt(iter);
+	struct kvm_mmu_page *root = sptep_to_sp(root_pt);
+	int as_id = kvm_mmu_page_as_id(root);
+
+	*iter->sptep = new_spte;
+
+	handle_changed_spte(kvm, as_id, iter->gfn, iter->old_spte, new_spte,
+			    iter->level);
+}
+
+#define tdp_root_for_each_pte(_iter, _root, _start, _end) \
+	for_each_tdp_pte(_iter, _root->spt, _root->role.level, _start, _end)
+
+/*
+ * Flush the TLB if the process should drop kvm->mmu_lock.
+ * Return whether the caller still needs to flush the tlb.
+ */
+static bool tdp_mmu_iter_flush_cond_resched(struct kvm *kvm, struct tdp_iter *iter)
+{
+	if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
+		kvm_flush_remote_tlbs(kvm);
+		cond_resched_lock(&kvm->mmu_lock);
+		tdp_iter_refresh_walk(iter);
+		return false;
+	} else {
+		return true;
+	}
+}
+
+/*
+ * Tears down the mappings for the range of gfns, [start, end), and frees the
+ * non-root pages mapping GFNs strictly within that range. Returns true if
+ * SPTEs have been cleared and a TLB flush is needed before releasing the
+ * MMU lock.
+ */
+static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
+			  gfn_t start, gfn_t end)
+{
+	struct tdp_iter iter;
+	bool flush_needed = false;
+
+	tdp_root_for_each_pte(iter, root, start, end) {
+		if (!is_shadow_present_pte(iter.old_spte))
+			continue;
+
+		/*
+		 * If this is a non-last-level SPTE that covers a larger range
+		 * than should be zapped, continue, and zap the mappings at a
+		 * lower level.
+		 */
+		if ((iter.gfn < start ||
+		     iter.gfn + KVM_PAGES_PER_HPAGE(iter.level) > end) &&
+		    !is_last_spte(iter.old_spte, iter.level))
+			continue;
+
+		tdp_mmu_set_spte(kvm, &iter, 0);
+
+		flush_needed = tdp_mmu_iter_flush_cond_resched(kvm, &iter);
+	}
+	return flush_needed;
+}
+
+/*
+ * Tears down the mappings for the range of gfns, [start, end), and frees the
+ * non-root pages mapping GFNs strictly within that range. Returns true if
+ * SPTEs have been cleared and a TLB flush is needed before releasing the
+ * MMU lock.
+ */
+bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+	struct kvm_mmu_page *root;
+	bool flush = false;
+
+	for_each_tdp_mmu_root(kvm, root) {
+		/*
+		 * Take a reference on the root so that it cannot be freed if
+		 * this thread releases the MMU lock and yields in this loop.
+		 */
+		kvm_mmu_get_root(kvm, root);
+
+		flush |= zap_gfn_range(kvm, root, start, end);
+
+		kvm_mmu_put_root(kvm, root);
+	}
+
+	return flush;
+}
+
+void kvm_tdp_mmu_zap_all(struct kvm *kvm)
+{
+	gfn_t max_gfn = 1ULL << (boot_cpu_data.x86_phys_bits - PAGE_SHIFT);
+	bool flush;
+
+	flush = kvm_tdp_mmu_zap_gfn_range(kvm, 0, max_gfn);
+	if (flush)
+		kvm_flush_remote_tlbs(kvm);
+}

arch/x86/kvm/mmu/tdp_mmu.h

@@ -12,4 +12,6 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
 hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
 void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root);
 
+bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end);
+void kvm_tdp_mmu_zap_all(struct kvm *kvm);
 #endif /* __KVM_X86_MMU_TDP_MMU_H */