[PATCH v2 2/5] perf kvm: Introduce guest interfaces for sampling callchains

[Tianyi Liu]

This patch introduces two callback interfaces used between perf and KVM:

- get_frame_pointer: Return the frame pointer of the running vm.

- read_virt: Read data from a virtual address of the running vm,
  used for reading the stack frames from the guest.

This also introduces a new flag, `PERF_GUEST_64BIT`, to the `.state`
callback interface, which indicates whether the vm is running in
64-bit mode.

Signed-off-by: Tianyi Liu <i.pear at outlook.com>
---
 include/linux/perf_event.h | 15 +++++++++++++++
 kernel/events/core.c       | 10 ++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e85cd1c0e..d0f937a62 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -28,10 +28,13 @@
 
 #define PERF_GUEST_ACTIVE	0x01
 #define PERF_GUEST_USER	0x02
+#define PERF_GUEST_64BIT 0x04
 
 struct perf_guest_info_callbacks {
 	unsigned int			(*state)(void);
 	unsigned long			(*get_ip)(void);
+	unsigned long			(*get_frame_pointer)(void);
+	bool				(*read_virt)(void *addr, void *dest, unsigned int len);
 	unsigned int			(*handle_intel_pt_intr)(void);
 };
 
@@ -1495,6 +1498,8 @@ extern struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 
 DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state);
 DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
+DECLARE_STATIC_CALL(__perf_guest_get_frame_pointer, *perf_guest_cbs->get_frame_pointer);
+DECLARE_STATIC_CALL(__perf_guest_read_virt, *perf_guest_cbs->read_virt);
 DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
 
 static inline unsigned int perf_guest_state(void)
@@ -1505,6 +1510,14 @@ static inline unsigned long perf_guest_get_ip(void)
 {
 	return static_call(__perf_guest_get_ip)();
 }
+static inline unsigned long perf_guest_get_frame_pointer(void)
+{
+	return static_call(__perf_guest_get_frame_pointer)();
+}
+static inline bool perf_guest_read_virt(void *addr, void *dest, unsigned int length)
+{
+	return static_call(__perf_guest_read_virt)(addr, dest, length);
+}
 static inline unsigned int perf_guest_handle_intel_pt_intr(void)
 {
 	return static_call(__perf_guest_handle_intel_pt_intr)();
@@ -1514,6 +1527,8 @@ extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callback
 #else
 static inline unsigned int perf_guest_state(void)		 { return 0; }
 static inline unsigned long perf_guest_get_ip(void)		 { return 0; }
+static inline unsigned long perf_guest_get_frame_pointer(void)	{ return 0; }
+static inline bool perf_guest_read_virt(void*, void*, unsigned int)	{ return 0; }
 static inline unsigned int perf_guest_handle_intel_pt_intr(void) { return 0; }
 #endif /* CONFIG_GUEST_PERF_EVENTS */
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4c72a41f1..eaba00ec2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6759,6 +6759,8 @@ struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 
 DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state);
 DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
+DEFINE_STATIC_CALL_RET0(__perf_guest_get_frame_pointer, *perf_guest_cbs->get_frame_pointer);
+DEFINE_STATIC_CALL_RET0(__perf_guest_read_virt, *perf_guest_cbs->read_virt);
 DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
 
 void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
@@ -6770,6 +6772,12 @@ void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 	static_call_update(__perf_guest_state, cbs->state);
 	static_call_update(__perf_guest_get_ip, cbs->get_ip);
 
+	if (cbs->get_frame_pointer)
+		static_call_update(__perf_guest_get_frame_pointer, cbs->get_frame_pointer);
+
+	if (cbs->read_virt)
+		static_call_update(__perf_guest_read_virt, cbs->read_virt);
+
 	/* Implementing ->handle_intel_pt_intr is optional. */
 	if (cbs->handle_intel_pt_intr)
 		static_call_update(__perf_guest_handle_intel_pt_intr,
@@ -6785,6 +6793,8 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 	rcu_assign_pointer(perf_guest_cbs, NULL);
 	static_call_update(__perf_guest_state, (void *)&__static_call_return0);
 	static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0);
+	static_call_update(__perf_guest_get_frame_pointer, (void *)&__static_call_return0);
+	static_call_update(__perf_guest_read_virt, (void *)&__static_call_return0);
 	static_call_update(__perf_guest_handle_intel_pt_intr,
 			   (void *)&__static_call_return0);
 	synchronize_rcu();
-- 
2.42.0