[PATCH 19/27] KVM: x86/mmu: Use page-track notifiers iff there are external users

Sean Christopherson
2022-12-23T01:00:40Z

Disable the page-track notifier code at compile time if there are no
external users, i.e. if CONFIG_KVM_EXTERNAL_WRITE_TRACKING=n. KVM itself
now hooks emulated writes directly instead of relying on the page-track
mechanism.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/include/asm/kvm_page_track.h | 2 ++
arch/x86/kvm/mmu/page_track.c | 9 ++++----
arch/x86/kvm/mmu/page_track.h | 30 +++++++++++++++++++++++----
4 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index eec424fac0ba..e8f8e1bd96c7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1223,7 +1223,9 @@ struct kvm_arch {
* create an NX huge page (without hanging the guest).
*/
struct list_head possible_nx_huge_pages;
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
struct kvm_page_track_notifier_head track_notifier_head;
+#endif
/*
* Protects marking pages unsync during page faults, as TDP MMU page
* faults only take mmu_lock for read. For simplicity, the unsync
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index deece45936a5..53c2adb25a07 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -55,6 +55,7 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
struct kvm_memory_slot *slot, gfn_t gfn,
enum kvm_page_track_mode mode);

+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
enum pg_level max_level);

@@ -64,5 +65,6 @@ kvm_page_track_register_notifier(struct kvm *kvm,
void
kvm_page_track_unregister_notifier(struct kvm *kvm,
struct kvm_page_track_notifier_node *n);
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */

#endif
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 2b302fd2c5dd..f932909aa9b5 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -193,6 +193,7 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
return !!READ_ONCE(slot->arch.gfn_track[mode][index]);
}

+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
void kvm_page_track_cleanup(struct kvm *kvm)
{
struct kvm_page_track_notifier_head *head;
@@ -208,6 +209,7 @@ int kvm_page_track_init(struct kvm *kvm)
head = &kvm->arch.track_notifier_head;
INIT_HLIST_HEAD(&head->track_notifier_list);
return init_srcu_struct(&head->track_srcu);
+ return 0;
}

/*
@@ -254,8 +256,8 @@ EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
* The node should figure out if the written page is the one that node is
* interested in by itself.
*/
-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
- int bytes)
+void __kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
+ int bytes)
{
struct kvm_page_track_notifier_head *head;
struct kvm_page_track_notifier_node *n;
@@ -272,8 +274,6 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
if (n->track_write)
n->track_write(gpa, new, bytes, n);
srcu_read_unlock(&head->track_srcu, idx);
-
- kvm_mmu_track_write(vcpu, gpa, new, bytes);
}

/*
@@ -316,3 +316,4 @@ enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
return max_level;
}
EXPORT_SYMBOL_GPL(kvm_page_track_max_mapping_level);
+#endif
diff --git a/arch/x86/kvm/mmu/page_track.h b/arch/x86/kvm/mmu/page_track.h
index 89712f123ad3..1b363784aa4a 100644
--- a/arch/x86/kvm/mmu/page_track.h
+++ b/arch/x86/kvm/mmu/page_track.h
@@ -6,8 +6,6 @@

#include <asm/kvm_page_track.h>

-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_alloc(struct kvm_memory_slot *slot);
@@ -21,13 +19,37 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
const struct kvm_memory_slot *slot,
gfn_t gfn, enum kvm_page_track_mode mode);

-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
- int bytes);
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
+int kvm_page_track_init(struct kvm *kvm);
+void kvm_page_track_cleanup(struct kvm *kvm);
+
+void __kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
+ int bytes);
void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot);

static inline bool kvm_page_track_has_external_user(struct kvm *kvm)
{
return hlist_empty(&kvm->arch.track_notifier_head.track_notifier_list);
}
+#else
+static inline int kvm_page_track_init(struct kvm *kvm) { return 0; }
+static inline void kvm_page_track_cleanup(struct kvm *kvm) { }
+
+static inline void __kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+ const u8 *new, int bytes) { }
+static inline void kvm_page_track_delete_slot(struct kvm *kvm,
+ struct kvm_memory_slot *slot) { }
+
+static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
+
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
+
+static inline void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+ const u8 *new, int bytes)
+{
+ __kvm_page_track_write(vcpu, gpa, new, bytes);
+
+ kvm_mmu_track_write(vcpu, gpa, new, bytes);
+}

#endif /* __KVM_X86_PAGE_TRACK_H */
--
2.39.0.314.g84b9a713c41-goog