[PATCH v3 4/5] perf kvm: Support sampling guest callchains

Tianyi Liu
2023-12-10T08:16:23Z

This patch provides support for sampling guests' callchains.

The signature of `get_perf_callchain` has been modified to explicitly
specify whether it needs to sample the host or guest callchain. Based on
the context, `get_perf_callchain` will distribute each sampling request
to one of `perf_callchain_user`, `perf_callchain_kernel`,
or `perf_callchain_guest`.

The reason for separately implementing `perf_callchain_user` and
`perf_callchain_kernel` is that the kernel may utilize special unwinders
like `ORC`. However, for the guest, we only support stackframe-based
unwinding, so the implementation is generic and only needs to be
separately implemented for 32-bit and 64-bit.

Signed-off-by: Tianyi Liu <i.pear@outlook.com>
---
arch/x86/events/core.c | 63 ++++++++++++++++++++++++++++++++------
include/linux/perf_event.h | 3 +-
kernel/bpf/stackmap.c | 8 ++---
kernel/events/callchain.c | 27 +++++++++++++++-
kernel/events/core.c | 7 ++++-
5 files changed, 91 insertions(+), 17 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 40ad1425ffa2..4ff412225217 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2758,11 +2758,6 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
struct unwind_state state;
unsigned long addr;

- if (perf_guest_state()) {
- /* TODO: We don't support guest os callchain now */
- return;
- }
-
if (perf_callchain_store(entry, regs->ip))
return;

@@ -2778,6 +2773,59 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
}
}

+static inline void
+perf_callchain_guest32(struct perf_callchain_entry_ctx *entry,
+ const struct perf_kvm_guest_unwind_info *unwind_info)
+{
+ unsigned long ss_base, cs_base;
+ struct stack_frame_ia32 frame;
+ const struct stack_frame_ia32 *fp;
+
+ cs_base = unwind_info->segment_cs_base;
+ ss_base = unwind_info->segment_ss_base;
+
+ fp = (void *)(ss_base + unwind_info->frame_pointer);
+ while (fp && entry->nr < entry->max_stack) {
+ if (!perf_guest_read_virt((unsigned long)&fp->next_frame,
+ &frame.next_frame, sizeof(frame.next_frame)))
+ break;
+ if (!perf_guest_read_virt((unsigned long)&fp->return_address,
+ &frame.return_address, sizeof(frame.return_address)))
+ break;
+ perf_callchain_store(entry, cs_base + frame.return_address);
+ fp = (void *)(ss_base + frame.next_frame);
+ }
+}
+
+void
+perf_callchain_guest(struct perf_callchain_entry_ctx *entry)
+{
+ struct stack_frame frame;
+ const struct stack_frame *fp;
+ struct perf_kvm_guest_unwind_info unwind_info;
+
+ if (!perf_guest_get_unwind_info(&unwind_info))
+ return;
+
+ perf_callchain_store(entry, unwind_info.ip_pointer);
+
+ if (unwind_info.is_guest_64bit) {
+ fp = (void *)unwind_info.frame_pointer;
+ while (fp && entry->nr < entry->max_stack) {
+ if (!perf_guest_read_virt((unsigned long)&fp->next_frame,
+ &frame.next_frame, sizeof(frame.next_frame)))
+ break;
+ if (!perf_guest_read_virt((unsigned long)&fp->return_address,
+ &frame.return_address, sizeof(frame.return_address)))
+ break;
+ perf_callchain_store(entry, frame.return_address);
+ fp = (void *)frame.next_frame;
+ }
+ } else {
+ perf_callchain_guest32(entry, &unwind_info);
+ }
+}
+
static inline int
valid_user_frame(const void __user *fp, unsigned long size)
{
@@ -2861,11 +2909,6 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
struct stack_frame frame;
const struct stack_frame __user *fp;

- if (perf_guest_state()) {
- /* TODO: We don't support guest os callchain now */
- return;
- }
-
/*
* We don't know what to do with VM86 stacks.. ignore them for now.
*/
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index dacc1623dcaa..483578672868 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1552,9 +1552,10 @@ DECLARE_PER_CPU(struct perf_callchain_entry, perf_callchain_entry);

extern void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs);
extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs);
+extern void perf_callchain_guest(struct perf_callchain_entry_ctx *entry);
extern struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
- u32 max_stack, bool crosstask, bool add_mark);
+ bool host, bool guest, u32 max_stack, bool crosstask, bool add_mark);
extern int get_callchain_buffers(int max_stack);
extern void put_callchain_buffers(void);
extern struct perf_callchain_entry *get_callchain_entry(int *rctx);
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index d6b277482085..5ca41ca08d8a 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -294,8 +294,8 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
if (max_depth > sysctl_perf_event_max_stack)
max_depth = sysctl_perf_event_max_stack;

- trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
- false, false);
+ trace = get_perf_callchain(regs, 0, kernel, user, true, false,
+ max_depth, false, false);

if (unlikely(!trace))
/* couldn't fetch the stack trace */
@@ -420,8 +420,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
else if (kernel && task)
trace = get_callchain_entry_for_task(task, max_depth);
else
- trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
- false, false);
+ trace = get_perf_callchain(regs, 0, kernel, user, true, false,
+ max_depth, false, false);
if (unlikely(!trace))
goto err_fault;

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 1273be84392c..7e80729e95d0 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -45,6 +45,10 @@ __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
{
}

+__weak void perf_callchain_guest(struct perf_callchain_entry_ctx *entry)
+{
+}
+
static void release_callchain_buffers_rcu(struct rcu_head *head)
{
struct callchain_cpus_entries *entries;
@@ -178,11 +182,12 @@ put_callchain_entry(int rctx)

struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
- u32 max_stack, bool crosstask, bool add_mark)
+ bool host, bool guest, u32 max_stack, bool crosstask, bool add_mark)
{
struct perf_callchain_entry *entry;
struct perf_callchain_entry_ctx ctx;
int rctx;
+ unsigned int guest_state;

entry = get_callchain_entry(&rctx);
if (!entry)
@@ -194,6 +199,26 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
ctx.contexts = 0;
ctx.contexts_maxed = false;

+ guest_state = perf_guest_state();
+ if (guest_state) {
+ if (!guest)
+ goto exit_put;
+ if (user && (guest_state & PERF_GUEST_USER)) {
+ if (add_mark)
+ perf_callchain_store_context(&ctx, PERF_CONTEXT_GUEST_USER);
+ perf_callchain_guest(&ctx);
+ }
+ if (kernel && !(guest_state & PERF_GUEST_USER)) {
+ if (add_mark)
+ perf_callchain_store_context(&ctx, PERF_CONTEXT_GUEST_KERNEL);
+ perf_callchain_guest(&ctx);
+ }
+ goto exit_put;
+ }
+
+ if (unlikely(!host))
+ goto exit_put;
+
if (kernel && !user_mode(regs)) {
if (add_mark)
perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4c5e35006217..3dea3fe840e6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7607,6 +7607,8 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
{
bool kernel = !event->attr.exclude_callchain_kernel;
bool user = !event->attr.exclude_callchain_user;
+ bool host = !event->attr.exclude_host;
+ bool guest = !event->attr.exclude_guest;
/* Disallow cross-task user callchains. */
bool crosstask = event->ctx->task && event->ctx->task != current;
const u32 max_stack = event->attr.sample_max_stack;
@@ -7615,7 +7617,10 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
if (!kernel && !user)
return &__empty_callchain;

- callchain = get_perf_callchain(regs, 0, kernel, user,
+ if (!host && !guest)
+ return &__empty_callchain;
+
+ callchain = get_perf_callchain(regs, 0, kernel, user, host, guest,
max_stack, crosstask, true);
return callchain ?: &__empty_callchain;
}
--
2.34.1