Re: [PATCH v3 07/16] perf: Add wrappers for invoking guest callbacks

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On 22/09/21 02:05, Sean Christopherson wrote:
Add helpers for the guest callbacks to prepare for burying the callbacks
behind a Kconfig (it's a lot easier to provide a few stubs than to #ifdef
piles of code), and also to prepare for converting the callbacks to
static_call().  perf_instruction_pointer() in particular will have subtle
semantics with static_call(), as the "no callbacks" case will return 0 if
the callbacks are unregistered between querying guest state and getting
the IP.  Implement the change now to avoid a functional change when adding
static_call() support, and because the new helper needs to return
_something_ in this case.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
  arch/arm64/kernel/perf_callchain.c | 16 +++++-----------
  arch/x86/events/core.c             | 15 +++++----------
  arch/x86/events/intel/core.c       |  5 +----
  include/linux/perf_event.h         | 24 ++++++++++++++++++++++++
  4 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 274dc3e11b6d..db04a55cee7e 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -102,9 +102,7 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
  void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
  			 struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state()) {
+	if (perf_guest_state()) {
  		/* We don't support guest os callchain now */
  		return;
  	}
@@ -149,10 +147,9 @@ static bool callchain_trace(void *data, unsigned long pc)
  void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
  			   struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
  	struct stackframe frame;
- if (guest_cbs && guest_cbs->state()) {
+	if (perf_guest_state()) {
  		/* We don't support guest os callchain now */
  		return;
  	}
@@ -163,18 +160,15 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
unsigned long perf_instruction_pointer(struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state())
-		return guest_cbs->get_ip();
+	if (perf_guest_state())
+		return perf_guest_get_ip();
return instruction_pointer(regs);
  }
unsigned long perf_misc_flags(struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
+	unsigned int guest_state = perf_guest_state();
  	int misc = 0;
if (guest_state) {
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 3a7630fdd340..d20e4f8d1aef 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2761,11 +2761,10 @@ static bool perf_hw_regs(struct pt_regs *regs)
  void
  perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
  	struct unwind_state state;
  	unsigned long addr;
- if (guest_cbs && guest_cbs->state()) {
+	if (perf_guest_state()) {
  		/* TODO: We don't support guest os callchain now */
  		return;
  	}
@@ -2865,11 +2864,10 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
  void
  perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
  	struct stack_frame frame;
  	const struct stack_frame __user *fp;
- if (guest_cbs && guest_cbs->state()) {
+	if (perf_guest_state()) {
  		/* TODO: We don't support guest os callchain now */
  		return;
  	}
@@ -2946,18 +2944,15 @@ static unsigned long code_segment_base(struct pt_regs *regs)
unsigned long perf_instruction_pointer(struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state())
-		return guest_cbs->get_ip();
+	if (perf_guest_state())
+		return perf_guest_get_ip();
return regs->ip + code_segment_base(regs);
  }
unsigned long perf_misc_flags(struct pt_regs *regs)
  {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
+	unsigned int guest_state = perf_guest_state();
  	int misc = 0;
if (guest_state) {
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 524ad1f747bd..f5b02017ba16 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2786,7 +2786,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
  {
  	struct perf_sample_data data;
  	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
-	struct perf_guest_info_callbacks *guest_cbs;
  	int bit;
  	int handled = 0;
  	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
@@ -2853,9 +2852,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
  	 */
  	if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
  		handled++;
-
-		guest_cbs = perf_get_guest_cbs();
-		if (likely(!guest_cbs || !guest_cbs->handle_intel_pt_intr()))
+		if (!perf_guest_handle_intel_pt_intr())
  			intel_pt_interrupt();
  	}
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f9be88a47434..c0a6eaf55fb1 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1247,6 +1247,30 @@ static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
  	/* Prevent reloading between a !NULL check and dereferences. */
  	return READ_ONCE(perf_guest_cbs);
  }
+static inline unsigned int perf_guest_state(void)
+{
+	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
+
+	return guest_cbs ? guest_cbs->state() : 0;
+}
+static inline unsigned long perf_guest_get_ip(void)
+{
+	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
+
+	/*
+	 * Arbitrarily return '0' in the unlikely scenario that the callbacks
+	 * are unregistered between checking guest state and getting the IP.
+	 */
+	return guest_cbs ? guest_cbs->get_ip() : 0;
+}
+static inline unsigned int perf_guest_handle_intel_pt_intr(void)
+{
+	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
+
+	if (guest_cbs && guest_cbs->handle_intel_pt_intr)
+		return guest_cbs->handle_intel_pt_intr();
+	return 0;
+}
  extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
  extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);

Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>




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