[PATCH v6 5/5] perf: Correct perf sampling with guest VMs
Colton Lewis
coltonlewis at google.com
Wed Nov 6 06:56:02 AEDT 2024
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 = 0. This way any host-only events with exclude_guest
set will never see unexpected guest samples. The behaviour of events
with exclude_guest = 0 is unchanged.
Note that events configured to sample both host and guest may still
misattribute a PMI that arrived in the host as a guest event depending
on KVM arch and vendor behavior.
Signed-off-by: Colton Lewis <coltonlewis at google.com>
Acked-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Oliver Upton <oliver.upton at linux.dev>
---
arch/arm64/include/asm/perf_event.h | 4 ----
arch/arm64/kernel/perf_callchain.c | 28 ----------------------------
arch/x86/events/core.c | 16 ++++------------
include/linux/perf_event.h | 21 +++++++++++++++++++--
kernel/events/core.c | 21 +++++++++++++++++----
5 files changed, 40 insertions(+), 50 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) ®s->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 24910c625e3d..aae0c5eabf09 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -3005,9 +3005,6 @@ 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);
}
@@ -3034,17 +3031,12 @@ unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
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 772ad352856b..e207acdd9e73 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1655,8 +1655,9 @@ 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) \
@@ -1667,6 +1668,22 @@ 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 2c44ffd6f4d8..c62164a2ff23 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7022,13 +7022,26 @@ 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);
}
@@ -7849,7 +7862,7 @@ 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;
}
@@ -8013,7 +8026,7 @@ 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
--
2.47.0.199.ga7371fff76-goog
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