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perf/core: Correct perf sampling with guest VMs

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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@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20241113190156.2145593-6-coltonlewis@google.com
This commit is contained in:
Colton Lewis 2024-11-13 19:01:55 +00:00 committed by Ingo Molnar
parent baff01f3d7
commit 2c47e7a74f
5 changed files with 36 additions and 41 deletions
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4
arch/arm64/include/asm/perf_event.h
View File

@ -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

28
arch/arm64/kernel/perf_callchain.c
View File

@ -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;
}

3
arch/x86/events/core.c
View File

@ -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);
}

21
include/linux/perf_event.h
View File

@ -1676,8 +1676,9 @@ 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) \
@ -1688,6 +1689,22 @@ 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_ACTIVE))
return 0;
if (guest_state & PERF_GUEST_USER)
return PERF_RECORD_MISC_GUEST_USER;
else
return PERF_RECORD_MISC_GUEST_KERNEL;
}
# 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;

21
kernel/events/core.c
View File

@ -7026,13 +7026,26 @@ 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);
}
@ -7853,7 +7866,7 @@ 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;
}
@ -8017,7 +8030,7 @@ 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