[RFC PATCH v2 01/10] KVM: x86: mmu: allow to enable write tracking externally

[Maxim Levitsky <mlevitsk@redhat.com>]

This will be used to enable write tracking from nested AVIC code
and can also be used to enable write tracking in GVT-g module
when it actually uses it as opposed to always enabling it,
when the module is compiled in the kernel.

No functional change intended.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/include/asm/kvm_host.h       |  2 +-
 arch/x86/include/asm/kvm_page_track.h |  1 +
 arch/x86/kvm/mmu.h                    |  8 +++++---
 arch/x86/kvm/mmu/mmu.c                | 17 ++++++++++-------
 arch/x86/kvm/mmu/page_track.c         | 10 ++++++++--
 5 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2c20f715f0094..ae41d2df69fe9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1234,7 +1234,7 @@ struct kvm_arch {
 	 * is used as one input when determining whether certain memslot
 	 * related allocations are necessary.
 	 */
-	bool shadow_root_allocated;
+	bool mmu_page_tracking_enabled;
 
 #if IS_ENABLED(CONFIG_HYPERV)
 	hpa_t	hv_root_tdp;
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index eb186bc57f6a9..955a5ae07b10e 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -50,6 +50,7 @@ int kvm_page_track_init(struct kvm *kvm);
 void kvm_page_track_cleanup(struct kvm *kvm);
 
 bool kvm_page_track_write_tracking_enabled(struct kvm *kvm);
+int kvm_page_track_write_tracking_enable(struct kvm *kvm);
 int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot);
 
 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot);
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 671cfeccf04e9..44d15551f7156 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -269,7 +269,7 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
 int kvm_mmu_post_init_vm(struct kvm *kvm);
 void kvm_mmu_pre_destroy_vm(struct kvm *kvm);
 
-static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
+static inline bool mmu_page_tracking_enabled(struct kvm *kvm)
 {
 	/*
 	 * Read shadow_root_allocated before related pointers. Hence, threads
@@ -277,9 +277,11 @@ static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
 	 * see the pointers. Pairs with smp_store_release in
 	 * mmu_first_shadow_root_alloc.
 	 */
-	return smp_load_acquire(&kvm->arch.shadow_root_allocated);
+	return smp_load_acquire(&kvm->arch.mmu_page_tracking_enabled);
 }
 
+int mmu_enable_write_tracking(struct kvm *kvm);
+
 #ifdef CONFIG_X86_64
 static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
 #else
@@ -288,7 +290,7 @@ static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
 
 static inline bool kvm_memslots_have_rmaps(struct kvm *kvm)
 {
-	return !is_tdp_mmu_enabled(kvm) || kvm_shadow_root_allocated(kvm);
+	return !is_tdp_mmu_enabled(kvm) || mmu_page_tracking_enabled(kvm);
 }
 
 static inline gfn_t gfn_to_index(gfn_t gfn, gfn_t base_gfn, int level)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 69a30d6d1e2b9..2c4edae4b026d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3368,7 +3368,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 	return r;
 }
 
-static int mmu_first_shadow_root_alloc(struct kvm *kvm)
+int mmu_enable_write_tracking(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
 	struct kvm_memory_slot *slot;
@@ -3378,21 +3378,20 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
 	 * Check if this is the first shadow root being allocated before
 	 * taking the lock.
 	 */
-	if (kvm_shadow_root_allocated(kvm))
+	if (mmu_page_tracking_enabled(kvm))
 		return 0;
 
 	mutex_lock(&kvm->slots_arch_lock);
 
 	/* Recheck, under the lock, whether this is the first shadow root. */
-	if (kvm_shadow_root_allocated(kvm))
+	if (mmu_page_tracking_enabled(kvm))
 		goto out_unlock;
 
 	/*
 	 * Check if anything actually needs to be allocated, e.g. all metadata
 	 * will be allocated upfront if TDP is disabled.
 	 */
-	if (kvm_memslots_have_rmaps(kvm) &&
-	    kvm_page_track_write_tracking_enabled(kvm))
+	if (kvm_memslots_have_rmaps(kvm) && mmu_page_tracking_enabled(kvm))
 		goto out_success;
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
@@ -3422,7 +3421,7 @@ static int mmu_first_shadow_root_alloc(struct kvm *kvm)
 	 * all the related pointers are set.
 	 */
 out_success:
-	smp_store_release(&kvm->arch.shadow_root_allocated, true);
+	smp_store_release(&kvm->arch.mmu_page_tracking_enabled, true);
 
 out_unlock:
 	mutex_unlock(&kvm->slots_arch_lock);
@@ -3459,7 +3458,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	r = mmu_first_shadow_root_alloc(vcpu->kvm);
+	r = mmu_enable_write_tracking(vcpu->kvm);
 	if (r)
 		return r;
 
@@ -5727,6 +5726,10 @@ int kvm_mmu_init_vm(struct kvm *kvm)
 	node->track_write = kvm_mmu_pte_write;
 	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
 	kvm_page_track_register_notifier(kvm, node);
+
+	if (IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) || !tdp_enabled)
+		mmu_enable_write_tracking(kvm);
+
 	return 0;
 }
 
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 2e09d1b6249f3..8857d629036d7 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -21,10 +21,16 @@
 
 bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)
 {
-	return IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) ||
-	       !tdp_enabled || kvm_shadow_root_allocated(kvm);
+	return mmu_page_tracking_enabled(kvm);
 }
 
+int kvm_page_track_write_tracking_enable(struct kvm *kvm)
+{
+	return mmu_enable_write_tracking(kvm);
+}
+EXPORT_SYMBOL_GPL(kvm_page_track_write_tracking_enable);
+
+
 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
 {
 	int i;
-- 
2.26.3