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Message-ID: <ce964b43f926708f30c85640591b2fc62397b719.camel@redhat.com>
Date: Tue, 10 Oct 2023 19:12:11 +0300
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Tianyi Liu <i.pear@...look.com>, seanjc@...gle.com,
pbonzini@...hat.com, peterz@...radead.org, mingo@...hat.com,
acme@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
kvm@...r.kernel.org, x86@...nel.org, mark.rutland@....com,
alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
namhyung@...nel.org, irogers@...gle.com, adrian.hunter@...el.com
Subject: Re: [PATCH v2 4/5] perf kvm: Support sampling guest callchains
У нд, 2023-10-08 у 22:57 +0800, Tianyi Liu пише:
> 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, it will distribute the 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
> such as `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@...look.com>
> ---
> arch/x86/events/core.c | 56 +++++++++++++++++++++++++++++++-------
> include/linux/perf_event.h | 3 +-
> kernel/bpf/stackmap.c | 8 +++---
> kernel/events/callchain.c | 27 +++++++++++++++++-
> kernel/events/core.c | 7 ++++-
> 5 files changed, 84 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 185f902e5..ea4c86175 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 +2773,52 @@ 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)
> +{
> + struct stack_frame_ia32 frame;
> + const struct stack_frame_ia32 *fp;
> +
> + fp = (void *)perf_guest_get_frame_pointer();
> + while (fp && entry->nr < entry->max_stack) {
> + if (!perf_guest_read_virt(&fp->next_frame, &frame.next_frame,
This should be fp->next_frame.
> + sizeof(frame.next_frame)))
> + break;
> + if (!perf_guest_read_virt(&fp->return_address, &frame.return_address,
Same here.
> + sizeof(frame.return_address)))
> + break;
> + perf_callchain_store(entry, frame.return_address);
> + fp = (void *)frame.next_frame;
> + }
> +}
> +
> +void
> +perf_callchain_guest(struct perf_callchain_entry_ctx *entry)
> +{
> + struct stack_frame frame;
> + const struct stack_frame *fp;
> + unsigned int guest_state;
> +
> + guest_state = perf_guest_state();
> + perf_callchain_store(entry, perf_guest_get_ip());
> +
> + if (guest_state & PERF_GUEST_64BIT) {
> + fp = (void *)perf_guest_get_frame_pointer();
> + while (fp && entry->nr < entry->max_stack) {
> + if (!perf_guest_read_virt(&fp->next_frame, &frame.next_frame,
Same here.
> + sizeof(frame.next_frame)))
> + break;
> + if (!perf_guest_read_virt(&fp->return_address, &frame.return_address,
And here.
> + sizeof(frame.return_address)))
> + break;
> + perf_callchain_store(entry, frame.return_address);
> + fp = (void *)frame.next_frame;
> + }
> + } else {
> + perf_callchain_guest32(entry);
> + }
> +}
For symmetry, maybe it makes sense to have perf_callchain_guest32 and perf_callchain_guest64
and then make perf_callchain_guest call each? No strong opinion on this of course.
> +
> static inline int
> valid_user_frame(const void __user *fp, unsigned long size)
> {
> @@ -2861,11 +2902,6 @@ 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 d0f937a62..a2baf4856 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1545,9 +1545,10 @@ 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 458bb80b1..2e88d4639 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 1273be843..7e80729e9 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 eaba00ec2..b3401f403 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7559,6 +7559,8 @@ 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;
> @@ -7567,7 +7569,10 @@ 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;
> }
Best regards,
Maxim Levitsky
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