[PATCH v2 0/5] Correct perf sampling with Guest VMs

[PATCH v2 0/5] Correct perf sampling with Guest VMs

[Colton Lewis]

v2:
  * Better explain commit messages
  * Fix incorrect type in patch 2
  * Fix missing argument in call to common_misc_flags() in patch 5
  * Rebase to 6.11-rc7 and include base commit in letter

v1:
https://lore.kernel.org/kvm/20240904204133.1442132-1-coltonlewis@google.com/

This series cleans up perf recording around guest events and improves
the accuracy of the resulting perf reports.

Perf was incorrectly counting any PMU overflow interrupt that occurred
while a VCPU was loaded as a guest event even when the events were not
truely guest events. This lead to much less accurate and useful perf
recordings.

See as an example the below reports of `perf record
dirty_log_perf_test -m 2 -v 4` before and after the series on ARM64.

Without series:

Samples: 15K of event 'instructions', Event count (approx.): 31830580924
Overhead  Command          Shared Object        Symbol
  54.54%  dirty_log_perf_  dirty_log_perf_test  [.] run_test
   5.39%  dirty_log_perf_  dirty_log_perf_test  [.] vcpu_worker
   0.89%  dirty_log_perf_  [kernel.vmlinux]     [k] release_pages
   0.70%  dirty_log_perf_  [kernel.vmlinux]     [k] free_pcppages_bulk
   0.62%  dirty_log_perf_  dirty_log_perf_test  [.] userspace_mem_region_find
   0.49%  dirty_log_perf_  dirty_log_perf_test  [.] sparsebit_is_set
   0.46%  dirty_log_perf_  dirty_log_perf_test  [.] _virt_pg_map
   0.46%  dirty_log_perf_  dirty_log_perf_test  [.] node_add
   0.37%  dirty_log_perf_  dirty_log_perf_test  [.] node_reduce
   0.35%  dirty_log_perf_  [kernel.vmlinux]     [k] free_unref_page_commit
   0.33%  dirty_log_perf_  [kernel.vmlinux]     [k] __kvm_pgtable_walk
   0.31%  dirty_log_perf_  [kernel.vmlinux]     [k] stage2_attr_walker
   0.29%  dirty_log_perf_  [kernel.vmlinux]     [k] unmap_page_range
   0.29%  dirty_log_perf_  dirty_log_perf_test  [.] test_assert
   0.26%  dirty_log_perf_  [kernel.vmlinux]     [k] __mod_memcg_lruvec_state
   0.24%  dirty_log_perf_  [kernel.vmlinux]     [k] kvm_s2_put_page

With series:

Samples: 15K of event 'instructions', Event count (approx.): 31830580924
Samples: 15K of event 'instructions', Event count (approx.): 30898031385
Overhead  Command          Shared Object        Symbol
  54.05%  dirty_log_perf_  dirty_log_perf_test  [.] run_test
   5.48%  dirty_log_perf_  [kernel.kallsyms]    [k] kvm_arch_vcpu_ioctl_run
   4.70%  dirty_log_perf_  dirty_log_perf_test  [.] vcpu_worker
   3.11%  dirty_log_perf_  [kernel.kallsyms]    [k] kvm_handle_guest_abort
   2.24%  dirty_log_perf_  [kernel.kallsyms]    [k] up_read
   1.98%  dirty_log_perf_  [kernel.kallsyms]    [k] __kvm_tlb_flush_vmid_ipa_nsh
   1.97%  dirty_log_perf_  [kernel.kallsyms]    [k] __pi_clear_page
   1.30%  dirty_log_perf_  [kernel.kallsyms]    [k] down_read
   1.13%  dirty_log_perf_  [kernel.kallsyms]    [k] release_pages
   1.12%  dirty_log_perf_  [kernel.kallsyms]    [k] __kvm_pgtable_walk
   1.08%  dirty_log_perf_  [kernel.kallsyms]    [k] folio_batch_move_lru
   1.06%  dirty_log_perf_  [kernel.kallsyms]    [k] __srcu_read_lock
   1.03%  dirty_log_perf_  [kernel.kallsyms]    [k] get_page_from_freelist
   1.01%  dirty_log_perf_  [kernel.kallsyms]    [k] __pte_offset_map_lock
   0.82%  dirty_log_perf_  [kernel.kallsyms]    [k] handle_mm_fault
   0.74%  dirty_log_perf_  [kernel.kallsyms]    [k] mas_state_walk

Colton Lewis (5):
  arm: perf: Drop unused functions
  perf: Hoist perf_instruction_pointer() and perf_misc_flags()
  powerpc: perf: Use perf_arch_instruction_pointer()
  x86: perf: Refactor misc flag assignments
  perf: Correct perf sampling with guest VMs

 arch/arm/include/asm/perf_event.h            |  7 ---
 arch/arm/kernel/perf_callchain.c             | 17 -------
 arch/arm64/include/asm/perf_event.h          |  4 --
 arch/arm64/kernel/perf_callchain.c           | 28 ------------
 arch/powerpc/include/asm/perf_event_server.h |  6 +--
 arch/powerpc/perf/callchain.c                |  2 +-
 arch/powerpc/perf/callchain_32.c             |  2 +-
 arch/powerpc/perf/callchain_64.c             |  2 +-
 arch/powerpc/perf/core-book3s.c              |  4 +-
 arch/s390/include/asm/perf_event.h           |  6 +--
 arch/s390/kernel/perf_event.c                |  4 +-
 arch/x86/events/core.c                       | 48 ++++++++++++--------
 arch/x86/include/asm/perf_event.h            | 12 +++--
 include/linux/perf_event.h                   | 26 +++++++++--
 kernel/events/core.c                         | 27 ++++++++++-
 15 files changed, 96 insertions(+), 99 deletions(-)


base-commit: da3ea35007d0af457a0afc87e84fddaebc4e0b63
--
2.46.0.598.g6f2099f65c-goog

[PATCH v2 1/5] arm: perf: Drop unused functions

[Colton Lewis]

For arm's implementation, perf_instruction_pointer() and
perf_misc_flags() are equivalent to the generic versions in
include/linux/perf_event.h so arch/arm doesn't need to provide its
own versions. Drop them here.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/arm/include/asm/perf_event.h |  7 -------
 arch/arm/kernel/perf_callchain.c  | 17 -----------------
 2 files changed, 24 deletions(-)

diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
index bdbc1e590891..c08f16f2e243 100644
--- a/arch/arm/include/asm/perf_event.h
+++ b/arch/arm/include/asm/perf_event.h
@@ -8,13 +8,6 @@
 #ifndef __ARM_PERF_EVENT_H__
 #define __ARM_PERF_EVENT_H__

-#ifdef CONFIG_PERF_EVENTS
-struct pt_regs;
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-#define perf_misc_flags(regs)	perf_misc_flags(regs)
-#endif
-
 #define perf_arch_fetch_caller_regs(regs, __ip) { \
 	(regs)->ARM_pc = (__ip); \
 	frame_pointer((regs)) = (unsigned long) __builtin_frame_address(0); \
diff --git a/arch/arm/kernel/perf_callchain.c b/arch/arm/kernel/perf_callchain.c
index 1d230ac9d0eb..a2601b1ef318 100644
--- a/arch/arm/kernel/perf_callchain.c
+++ b/arch/arm/kernel/perf_callchain.c
@@ -96,20 +96,3 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
 	arm_get_current_stackframe(regs, &fr);
 	walk_stackframe(&fr, callchain_trace, entry);
 }
-
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
-{
-	return instruction_pointer(regs);
-}
-
-unsigned long perf_misc_flags(struct pt_regs *regs)
-{
-	int misc = 0;
-
-	if (user_mode(regs))
-		misc |= PERF_RECORD_MISC_USER;
-	else
-		misc |= PERF_RECORD_MISC_KERNEL;
-
-	return misc;
-}
--
2.46.0.598.g6f2099f65c-goog

[PATCH v2 2/5] perf: Hoist perf_instruction_pointer() and perf_misc_flags()

[Colton Lewis]

For clarity, rename the arch-specific definitions of these functions
to perf_arch_* to denote they are arch-specifc. Define the
generic-named functions in one place where they can call the
arch-specific ones as needed.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/arm64/include/asm/perf_event.h          |  6 +++---
 arch/arm64/kernel/perf_callchain.c           |  4 ++--
 arch/powerpc/include/asm/perf_event_server.h |  6 +++---
 arch/powerpc/perf/core-book3s.c              |  4 ++--
 arch/s390/include/asm/perf_event.h           |  6 +++---
 arch/s390/kernel/perf_event.c                |  4 ++--
 arch/x86/events/core.c                       |  4 ++--
 arch/x86/include/asm/perf_event.h            | 10 +++++-----
 include/linux/perf_event.h                   |  9 ++++++---
 kernel/events/core.c                         | 10 ++++++++++
 10 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index eb7071c9eb34..31a5584ed423 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h
@@ -11,9 +11,9 @@
 
 #ifdef CONFIG_PERF_EVENTS
 struct pt_regs;
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-#define perf_misc_flags(regs)	perf_misc_flags(regs)
+extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
+extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+#define perf_arch_misc_flags(regs)	perf_misc_flags(regs)
 #define perf_arch_bpf_user_pt_regs(regs) &regs->user_regs
 #endif
 
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index e8ed5673f481..01a9d08fc009 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -39,7 +39,7 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 	arch_stack_walk(callchain_trace, entry, current, regs);
 }
 
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
+unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 {
 	if (perf_guest_state())
 		return perf_guest_get_ip();
@@ -47,7 +47,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
 	return instruction_pointer(regs);
 }
 
-unsigned long perf_misc_flags(struct pt_regs *regs)
+unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	unsigned int guest_state = perf_guest_state();
 	int misc = 0;
diff --git a/arch/powerpc/include/asm/perf_event_server.h b/arch/powerpc/include/asm/perf_event_server.h
index 5995614e9062..41587d3f8446 100644
--- a/arch/powerpc/include/asm/perf_event_server.h
+++ b/arch/powerpc/include/asm/perf_event_server.h
@@ -102,8 +102,8 @@ struct power_pmu {
 int __init register_power_pmu(struct power_pmu *pmu);
 
 struct pt_regs;
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
+extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
 extern unsigned long int read_bhrb(int n);
 
 /*
@@ -111,7 +111,7 @@ extern unsigned long int read_bhrb(int n);
  * if we have hardware PMU support.
  */
 #ifdef CONFIG_PPC_PERF_CTRS
-#define perf_misc_flags(regs)	perf_misc_flags(regs)
+#define perf_arch_misc_flags(regs)	perf_misc_flags(regs)
 #endif
 
 /*
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 42867469752d..dc01aa604cc1 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2332,7 +2332,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
  * Called from generic code to get the misc flags (i.e. processor mode)
  * for an event_id.
  */
-unsigned long perf_misc_flags(struct pt_regs *regs)
+unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	u32 flags = perf_get_misc_flags(regs);
 
@@ -2346,7 +2346,7 @@ unsigned long perf_misc_flags(struct pt_regs *regs)
  * Called from generic code to get the instruction pointer
  * for an event_id.
  */
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
+unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 {
 	unsigned long siar = mfspr(SPRN_SIAR);
 
diff --git a/arch/s390/include/asm/perf_event.h b/arch/s390/include/asm/perf_event.h
index 9917e2717b2b..f2d83289ec7a 100644
--- a/arch/s390/include/asm/perf_event.h
+++ b/arch/s390/include/asm/perf_event.h
@@ -37,9 +37,9 @@ extern ssize_t cpumf_events_sysfs_show(struct device *dev,
 
 /* Perf callbacks */
 struct pt_regs;
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-#define perf_misc_flags(regs) perf_misc_flags(regs)
+extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
+extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+#define perf_arch_misc_flags(regs) perf_misc_flags(regs)
 #define perf_arch_bpf_user_pt_regs(regs) &regs->user_regs
 
 /* Perf pt_regs extension for sample-data-entry indicators */
diff --git a/arch/s390/kernel/perf_event.c b/arch/s390/kernel/perf_event.c
index 5fff629b1a89..f9000ab49f4a 100644
--- a/arch/s390/kernel/perf_event.c
+++ b/arch/s390/kernel/perf_event.c
@@ -57,7 +57,7 @@ static unsigned long instruction_pointer_guest(struct pt_regs *regs)
 	return sie_block(regs)->gpsw.addr;
 }
 
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
+unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 {
 	return is_in_guest(regs) ? instruction_pointer_guest(regs)
 				 : instruction_pointer(regs);
@@ -84,7 +84,7 @@ static unsigned long perf_misc_flags_sf(struct pt_regs *regs)
 	return flags;
 }
 
-unsigned long perf_misc_flags(struct pt_regs *regs)
+unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	/* Check if the cpum_sf PMU has created the pt_regs structure.
 	 * In this case, perf misc flags can be easily extracted.  Otherwise,
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index be01823b1bb4..760ad067527c 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2940,7 +2940,7 @@ static unsigned long code_segment_base(struct pt_regs *regs)
 	return 0;
 }
 
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
+unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 {
 	if (perf_guest_state())
 		return perf_guest_get_ip();
@@ -2948,7 +2948,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
 	return regs->ip + code_segment_base(regs);
 }
 
-unsigned long perf_misc_flags(struct pt_regs *regs)
+unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	unsigned int guest_state = perf_guest_state();
 	int misc = 0;
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 91b73571412f..feb87bf3d2e9 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -536,15 +536,15 @@ struct x86_perf_regs {
 	u64		*xmm_regs;
 };
 
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-#define perf_misc_flags(regs)	perf_misc_flags(regs)
+extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
+extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+#define perf_arch_misc_flags(regs)	perf_arch_misc_flags(regs)
 
 #include <asm/stacktrace.h>
 
 /*
- * We abuse bit 3 from flags to pass exact information, see perf_misc_flags
- * and the comment with PERF_EFLAGS_EXACT.
+ * We abuse bit 3 from flags to pass exact information, see
+ * perf_arch_misc_flags() and the comment with PERF_EFLAGS_EXACT.
  */
 #define perf_arch_fetch_caller_regs(regs, __ip)		{	\
 	(regs)->ip = (__ip);					\
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 1a8942277dda..d061e327ad54 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1633,10 +1633,13 @@ extern void perf_tp_event(u16 event_type, u64 count, void *record,
 			  struct task_struct *task);
 extern void perf_bp_event(struct perf_event *event, void *data);
 
-#ifndef perf_misc_flags
-# define perf_misc_flags(regs) \
+extern unsigned long perf_misc_flags(struct pt_regs *regs);
+extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
+
+#ifndef perf_arch_misc_flags
+# define perf_arch_misc_flags(regs) \
 		(user_mode(regs) ? PERF_RECORD_MISC_USER : PERF_RECORD_MISC_KERNEL)
-# define perf_instruction_pointer(regs)	instruction_pointer(regs)
+# define perf_arch_instruction_pointer(regs)	instruction_pointer(regs)
 #endif
 #ifndef perf_arch_bpf_user_pt_regs
 # define perf_arch_bpf_user_pt_regs(regs) regs
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8a6c6bbcd658..eeabbf791a8c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6921,6 +6921,16 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
 #endif
 
+unsigned long perf_misc_flags(struct pt_regs *regs)
+{
+	return perf_arch_misc_flags(regs);
+}
+
+unsigned long perf_instruction_pointer(struct pt_regs *regs)
+{
+	return perf_arch_instruction_pointer(regs);
+}
+
 static void
 perf_output_sample_regs(struct perf_output_handle *handle,
 			struct pt_regs *regs, u64 mask)
-- 
2.46.0.598.g6f2099f65c-goog

[PATCH v2 3/5] powerpc: perf: Use perf_arch_instruction_pointer()

[Colton Lewis]

Make sure powerpc uses the arch-specific function now that those have
been reorganized.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/powerpc/perf/callchain.c    | 2 +-
 arch/powerpc/perf/callchain_32.c | 2 +-
 arch/powerpc/perf/callchain_64.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
index 6b4434dd0ff3..26aa26482c9a 100644
--- a/arch/powerpc/perf/callchain.c
+++ b/arch/powerpc/perf/callchain.c
@@ -51,7 +51,7 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
 
 	lr = regs->link;
 	sp = regs->gpr[1];
-	perf_callchain_store(entry, perf_instruction_pointer(regs));
+	perf_callchain_store(entry, perf_arch_instruction_pointer(regs));
 
 	if (!validate_sp(sp, current))
 		return;
diff --git a/arch/powerpc/perf/callchain_32.c b/arch/powerpc/perf/callchain_32.c
index ea8cfe3806dc..ddcc2d8aa64a 100644
--- a/arch/powerpc/perf/callchain_32.c
+++ b/arch/powerpc/perf/callchain_32.c
@@ -139,7 +139,7 @@ void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
 	long level = 0;
 	unsigned int __user *fp, *uregs;
 
-	next_ip = perf_instruction_pointer(regs);
+	next_ip = perf_arch_instruction_pointer(regs);
 	lr = regs->link;
 	sp = regs->gpr[1];
 	perf_callchain_store(entry, next_ip);
diff --git a/arch/powerpc/perf/callchain_64.c b/arch/powerpc/perf/callchain_64.c
index 488e8a21a11e..115d1c105e8a 100644
--- a/arch/powerpc/perf/callchain_64.c
+++ b/arch/powerpc/perf/callchain_64.c
@@ -74,7 +74,7 @@ void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
 	struct signal_frame_64 __user *sigframe;
 	unsigned long __user *fp, *uregs;
 
-	next_ip = perf_instruction_pointer(regs);
+	next_ip = perf_arch_instruction_pointer(regs);
 	lr = regs->link;
 	sp = regs->gpr[1];
 	perf_callchain_store(entry, next_ip);
-- 
2.46.0.598.g6f2099f65c-goog

[PATCH v2 4/5] x86: perf: Refactor misc flag assignments

[Colton Lewis]

Break the assignment logic for misc flags into their own respective
functions to reduce the complexity of the nested logic.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/x86/events/core.c            | 31 +++++++++++++++++++++++--------
 arch/x86/include/asm/perf_event.h |  2 ++
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 760ad067527c..d51e5d24802b 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2948,16 +2948,34 @@ unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 	return regs->ip + code_segment_base(regs);
 }
 
+static unsigned long common_misc_flags(struct pt_regs *regs)
+{
+	if (regs->flags & PERF_EFLAGS_EXACT)
+		return PERF_RECORD_MISC_EXACT_IP;
+
+	return 0;
+}
+
+unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
+{
+	unsigned long guest_state = perf_guest_state();
+	unsigned long flags = common_misc_flags(regs);
+
+	if (guest_state & PERF_GUEST_USER)
+		flags |= PERF_RECORD_MISC_GUEST_USER;
+	else if (guest_state & PERF_GUEST_ACTIVE)
+		flags |= PERF_RECORD_MISC_GUEST_KERNEL;
+
+	return flags;
+}
+
 unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	unsigned int guest_state = perf_guest_state();
-	int misc = 0;
+	unsigned long misc = common_misc_flags(regs);
 
 	if (guest_state) {
-		if (guest_state & PERF_GUEST_USER)
-			misc |= PERF_RECORD_MISC_GUEST_USER;
-		else
-			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
+		misc |= perf_arch_guest_misc_flags(regs);
 	} else {
 		if (user_mode(regs))
 			misc |= PERF_RECORD_MISC_USER;
@@ -2965,9 +2983,6 @@ unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 			misc |= PERF_RECORD_MISC_KERNEL;
 	}
 
-	if (regs->flags & PERF_EFLAGS_EXACT)
-		misc |= PERF_RECORD_MISC_EXACT_IP;
-
 	return misc;
 }
 
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index feb87bf3d2e9..d95f902acc52 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -538,7 +538,9 @@ struct x86_perf_regs {
 
 extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
 extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+extern unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs);
 #define perf_arch_misc_flags(regs)	perf_arch_misc_flags(regs)
+#define perf_arch_guest_misc_flags(regs)	perf_arch_guest_misc_flags(regs)
 
 #include <asm/stacktrace.h>
 
-- 
2.46.0.598.g6f2099f65c-goog

[PATCH v2 5/5] perf: Correct perf sampling with guest VMs

[Colton Lewis]

Previously any PMU overflow interrupt that fired while a VCPU was
loaded was recorded as a guest event whether it truly was or not. This
resulted in nonsense perf recordings that did not honor
perf_event_attr.exclude_guest and recorded guest IPs where it should
have recorded host IPs.

Rework the sampling logic to only record guest samples for events with
exclude_guest clear. This way any host-only events with exclude_guest
set will never see unexpected guest samples. The behaviour of events
with exclude_guest clear is unchanged.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/arm64/include/asm/perf_event.h |  4 ----
 arch/arm64/kernel/perf_callchain.c  | 28 ----------------------------
 arch/x86/events/core.c              | 15 ++++-----------
 include/linux/perf_event.h          | 21 +++++++++++++++++++--
 kernel/events/core.c                | 21 +++++++++++++++++----
 5 files changed, 40 insertions(+), 49 deletions(-)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index 31a5584ed423..ee45b4e77347 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h
@@ -10,10 +10,6 @@
 #include <asm/ptrace.h>
 
 #ifdef CONFIG_PERF_EVENTS
-struct pt_regs;
-extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
-extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
-#define perf_arch_misc_flags(regs)	perf_misc_flags(regs)
 #define perf_arch_bpf_user_pt_regs(regs) &regs->user_regs
 #endif
 
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 01a9d08fc009..9b7f26b128b5 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -38,31 +38,3 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 
 	arch_stack_walk(callchain_trace, entry, current, regs);
 }
-
-unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
-{
-	if (perf_guest_state())
-		return perf_guest_get_ip();
-
-	return instruction_pointer(regs);
-}
-
-unsigned long perf_arch_misc_flags(struct pt_regs *regs)
-{
-	unsigned int guest_state = perf_guest_state();
-	int misc = 0;
-
-	if (guest_state) {
-		if (guest_state & PERF_GUEST_USER)
-			misc |= PERF_RECORD_MISC_GUEST_USER;
-		else
-			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
-	} else {
-		if (user_mode(regs))
-			misc |= PERF_RECORD_MISC_USER;
-		else
-			misc |= PERF_RECORD_MISC_KERNEL;
-	}
-
-	return misc;
-}
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d51e5d24802b..5f119b9516dc 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2942,9 +2942,6 @@ static unsigned long code_segment_base(struct pt_regs *regs)
 
 unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 {
-	if (perf_guest_state())
-		return perf_guest_get_ip();
-
 	return regs->ip + code_segment_base(regs);
 }
 
@@ -2974,14 +2971,10 @@ unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 	unsigned int guest_state = perf_guest_state();
 	unsigned long misc = common_misc_flags(regs);
 
-	if (guest_state) {
-		misc |= perf_arch_guest_misc_flags(regs);
-	} else {
-		if (user_mode(regs))
-			misc |= PERF_RECORD_MISC_USER;
-		else
-			misc |= PERF_RECORD_MISC_KERNEL;
-	}
+	if (user_mode(regs))
+		misc |= PERF_RECORD_MISC_USER;
+	else
+		misc |= PERF_RECORD_MISC_KERNEL;
 
 	return misc;
 }
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d061e327ad54..968f3edd95e4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1633,8 +1633,9 @@ extern void perf_tp_event(u16 event_type, u64 count, void *record,
 			  struct task_struct *task);
 extern void perf_bp_event(struct perf_event *event, void *data);
 
-extern unsigned long perf_misc_flags(struct pt_regs *regs);
-extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
+extern unsigned long perf_misc_flags(struct perf_event *event, struct pt_regs *regs);
+extern unsigned long perf_instruction_pointer(struct perf_event *event,
+					      struct pt_regs *regs);
 
 #ifndef perf_arch_misc_flags
 # define perf_arch_misc_flags(regs) \
@@ -1645,6 +1646,22 @@ extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
 # define perf_arch_bpf_user_pt_regs(regs) regs
 #endif
 
+#ifndef perf_arch_guest_misc_flags
+static inline unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
+{
+	unsigned long guest_state = perf_guest_state();
+
+	if (guest_state & PERF_GUEST_USER)
+		return PERF_RECORD_MISC_GUEST_USER;
+
+	if (guest_state & PERF_GUEST_ACTIVE)
+		return PERF_RECORD_MISC_GUEST_KERNEL;
+
+	return 0;
+}
+# define perf_arch_guest_misc_flags(regs)	perf_arch_guest_misc_flags(regs)
+#endif
+
 static inline bool has_branch_stack(struct perf_event *event)
 {
 	return event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index eeabbf791a8c..c5e57c024d9a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6921,13 +6921,26 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
 #endif
 
-unsigned long perf_misc_flags(struct pt_regs *regs)
+static bool should_sample_guest(struct perf_event *event)
 {
+	return !event->attr.exclude_guest && perf_guest_state();
+}
+
+unsigned long perf_misc_flags(struct perf_event *event,
+			      struct pt_regs *regs)
+{
+	if (should_sample_guest(event))
+		return perf_arch_guest_misc_flags(regs);
+
 	return perf_arch_misc_flags(regs);
 }
 
-unsigned long perf_instruction_pointer(struct pt_regs *regs)
+unsigned long perf_instruction_pointer(struct perf_event *event,
+				       struct pt_regs *regs)
 {
+	if (should_sample_guest(event))
+		return perf_guest_get_ip();
+
 	return perf_arch_instruction_pointer(regs);
 }
 
@@ -7743,7 +7756,7 @@ void perf_prepare_sample(struct perf_sample_data *data,
 	__perf_event_header__init_id(data, event, filtered_sample_type);
 
 	if (filtered_sample_type & PERF_SAMPLE_IP) {
-		data->ip = perf_instruction_pointer(regs);
+		data->ip = perf_instruction_pointer(event, regs);
 		data->sample_flags |= PERF_SAMPLE_IP;
 	}
 
@@ -7907,7 +7920,7 @@ void perf_prepare_header(struct perf_event_header *header,
 {
 	header->type = PERF_RECORD_SAMPLE;
 	header->size = perf_sample_data_size(data, event);
-	header->misc = perf_misc_flags(regs);
+	header->misc = perf_misc_flags(event, regs);
 
 	/*
 	 * If you're adding more sample types here, you likely need to do
-- 
2.46.0.598.g6f2099f65c-goog

Re: [PATCH v2 5/5] perf: Correct perf sampling with guest VMs

[Sean Christopherson]

On Wed, Sep 11, 2024, Colton Lewis wrote:
> Previously any PMU overflow interrupt that fired while a VCPU was
> loaded was recorded as a guest event whether it truly was or not. This
> resulted in nonsense perf recordings that did not honor
> perf_event_attr.exclude_guest and recorded guest IPs where it should
> have recorded host IPs.
> 
> Rework the sampling logic to only record guest samples for events with
> exclude_guest clear. This way any host-only events with exclude_guest
> set will never see unexpected guest samples. The behaviour of events
> with exclude_guest clear is unchanged.

Nit, "with exclude_guest clear" is easy to misread as simply "with exclude_guest"
(I did so at least three times).  Maybe 

  The behavior of exclude_guest=0 events is unchanged.

or

  The behavior of events without exclude_guest is unchanged.

I think it's also worth explicitly calling out that events that are configured
to sample both host and guest may still be prone to misattributing a PMI that
arrived in the host as a guest event, depending on the KVM arch and/or vendor
behavior.

Re: [PATCH v2 5/5] perf: Correct perf sampling with guest VMs

[Colton Lewis]

Sean Christopherson <seanjc@google.com> writes:

> On Wed, Sep 11, 2024, Colton Lewis wrote:
>> Previously any PMU overflow interrupt that fired while a VCPU was
>> loaded was recorded as a guest event whether it truly was or not. This
>> resulted in nonsense perf recordings that did not honor
>> perf_event_attr.exclude_guest and recorded guest IPs where it should
>> have recorded host IPs.

>> Rework the sampling logic to only record guest samples for events with
>> exclude_guest clear. This way any host-only events with exclude_guest
>> set will never see unexpected guest samples. The behaviour of events
>> with exclude_guest clear is unchanged.

> Nit, "with exclude_guest clear" is easy to misread as simply "with  
> exclude_guest"
> (I did so at least three times).  Maybe

>    The behavior of exclude_guest=0 events is unchanged.

> or

>    The behavior of events without exclude_guest is unchanged.

> I think it's also worth explicitly calling out that events that are  
> configured
> to sample both host and guest may still be prone to misattributing a PMI  
> that
> arrived in the host as a guest event, depending on the KVM arch and/or  
> vendor
> behavior.

Done