[PATCH v3 2/5] perf kvm: Introduce guest interfaces for sampling callchains

[Tianyi Liu]

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

- get_unwind_info: Return required data for unwinding at once; including
  ip address, frame pointer, whether the guest vCPU is running in 32 or 64
  bits, and possibly the base addresses of the segments.

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

Signed-off-by: Tianyi Liu <i.pear at outlook.com>
---
 include/linux/perf_event.h | 17 +++++++++++++++++
 kernel/events/core.c       | 10 ++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5547ba68e6e4..dacc1623dcaa 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -17,6 +17,8 @@
 #include <uapi/linux/perf_event.h>
 #include <uapi/linux/bpf_perf_event.h>
 
+#include <linux/perf_kvm.h>
+
 /*
  * Kernel-internal data types and definitions:
  */
@@ -32,6 +34,9 @@
 struct perf_guest_info_callbacks {
 	unsigned int			(*state)(void);
 	unsigned long			(*get_ip)(void);
+	bool				(*get_unwind_info)(struct perf_kvm_guest_unwind_info *info);
+	bool				(*read_virt)(unsigned long addr, void *dest,
+						     unsigned int len);
 	unsigned int			(*handle_intel_pt_intr)(void);
 };
 
@@ -1500,6 +1505,8 @@ 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_unwind_info, *perf_guest_cbs->get_unwind_info);
+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)
@@ -1510,6 +1517,14 @@ static inline unsigned long perf_guest_get_ip(void)
 {
 	return static_call(__perf_guest_get_ip)();
 }
+static inline bool perf_guest_get_unwind_info(struct perf_kvm_guest_unwind_info *info)
+{
+	return static_call(__perf_guest_get_unwind_info)(info);
+}
+static inline bool perf_guest_read_virt(unsigned long 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)();
@@ -1519,6 +1534,8 @@ 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 bool perf_guest_get_unwind_info(struct perf_kvm_guest_unwind_info *) { return 0; }
+static inline bool perf_guest_read_virt(unsigned long, 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 b704d83a28b2..4c5e35006217 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6807,6 +6807,8 @@ 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_unwind_info, *perf_guest_cbs->get_unwind_info);
+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)
@@ -6818,6 +6820,12 @@ 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_unwind_info)
+		static_call_update(__perf_guest_get_unwind_info, cbs->get_unwind_info);
+
+	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,
@@ -6833,6 +6841,8 @@ 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_unwind_info, (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();
-- 
2.34.1