[Intel-gfx] [PATCH v3 21/28] KVM: x86/mmu: Use page-track notifiers iff there are external users

Sean Christopherson
2023-05-13T00:37:00Z

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.

Provide a stub for "struct kvm_page_track_notifier_node" so that including
headers directly from the command line, e.g. for testing include guards,
doesn't fail due to a struct having an incomplete type.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/include/asm/kvm_page_track.h | 22 +++++++++++++-------
arch/x86/kvm/mmu/page_track.c | 10 ++++-----
arch/x86/kvm/mmu/page_track.h | 29 +++++++++++++++++++++++----
4 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 113598d3e886..5ce06a75d3de 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1247,7 +1247,9 @@ 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 76c0070dfe2a..61adb07b5927 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -9,6 +9,14 @@ enum kvm_page_track_mode {
KVM_PAGE_TRACK_MAX,
};

+void kvm_slot_page_track_add_page(struct kvm *kvm,
+ struct kvm_memory_slot *slot, gfn_t gfn,
+ enum kvm_page_track_mode mode);
+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
/*
* The notifier represented by @kvm_page_track_notifier_node is linked into
* the head which will be notified when guest is triggering the track event.
@@ -48,18 +56,18 @@ struct kvm_page_track_notifier_node {
struct kvm_page_track_notifier_node *node);
};

-void kvm_slot_page_track_add_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode);
-void kvm_slot_page_track_remove_page(struct kvm *kvm,
- struct kvm_memory_slot *slot, gfn_t gfn,
- enum kvm_page_track_mode mode);
-
void
kvm_page_track_register_notifier(struct kvm *kvm,
struct kvm_page_track_notifier_node *n);
void
kvm_page_track_unregister_notifier(struct kvm *kvm,
struct kvm_page_track_notifier_node *n);
+#else
+/*
+ * Allow defining a node in a structure even if page tracking is disabled, e.g.
+ * to play nice with testing headers via direct inclusion from the command line.
+ */
+struct kvm_page_track_notifier_node {};
+#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 e15329d48f95..b20aad7ac3fe 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -194,6 +194,7 @@ 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;
@@ -255,14 +256,13 @@ 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 *kvm, gpa_t gpa, const u8 *new, int bytes)
{
struct kvm_page_track_notifier_head *head;
struct kvm_page_track_notifier_node *n;
int idx;

- head = &vcpu->kvm->arch.track_notifier_head;
+ head = &kvm->arch.track_notifier_head;

if (hlist_empty(&head->track_notifier_list))
return;
@@ -273,8 +273,6 @@ 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);
}

/*
@@ -299,3 +297,5 @@ void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
n->track_remove_region(slot->base_gfn, slot->npages, n);
srcu_read_unlock(&head->track_srcu, idx);
}
+
+#endif
diff --git a/arch/x86/kvm/mmu/page_track.h b/arch/x86/kvm/mmu/page_track.h
index 89712f123ad3..931b26b8fc8f 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 +19,36 @@ 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 *kvm, 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 *kvm, 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->kvm, gpa, new, bytes);
+
+ kvm_mmu_track_write(vcpu, gpa, new, bytes);
+}

#endif /* __KVM_X86_PAGE_TRACK_H */
--
2.40.1.606.ga4b1b128d6-goog