Re: [PATCH v3 07/16] perf: Add wrappers for invoking guest callbacks

[Paolo Bonzini <pbonzini@redhat.com>]

On 22/09/21 02:05, Sean Christopherson wrote:
> Add helpers for the guest callbacks to prepare for burying the callbacks
> behind a Kconfig (it's a lot easier to provide a few stubs than to #ifdef
> piles of code), and also to prepare for converting the callbacks to
> static_call().  perf_instruction_pointer() in particular will have subtle
> semantics with static_call(), as the "no callbacks" case will return 0 if
> the callbacks are unregistered between querying guest state and getting
> the IP.  Implement the change now to avoid a functional change when adding
> static_call() support, and because the new helper needs to return
> _something_ in this case.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm64/kernel/perf_callchain.c | 16 +++++-----------
>   arch/x86/events/core.c             | 15 +++++----------
>   arch/x86/events/intel/core.c       |  5 +----
>   include/linux/perf_event.h         | 24 ++++++++++++++++++++++++
>   4 files changed, 35 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
> index 274dc3e11b6d..db04a55cee7e 100644
> --- a/arch/arm64/kernel/perf_callchain.c
> +++ b/arch/arm64/kernel/perf_callchain.c
> @@ -102,9 +102,7 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
>   void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>   			 struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	if (guest_cbs && guest_cbs->state()) {
> +	if (perf_guest_state()) {
>   		/* We don't support guest os callchain now */
>   		return;
>   	}
> @@ -149,10 +147,9 @@ static bool callchain_trace(void *data, unsigned long pc)
>   void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   			   struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct stackframe frame;
>   
> -	if (guest_cbs && guest_cbs->state()) {
> +	if (perf_guest_state()) {
>   		/* We don't support guest os callchain now */
>   		return;
>   	}
> @@ -163,18 +160,15 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>   
>   unsigned long perf_instruction_pointer(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	if (guest_cbs && guest_cbs->state())
> -		return guest_cbs->get_ip();
> +	if (perf_guest_state())
> +		return perf_guest_get_ip();
>   
>   	return instruction_pointer(regs);
>   }
>   
>   unsigned long perf_misc_flags(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
> +	unsigned int guest_state = perf_guest_state();
>   	int misc = 0;
>   
>   	if (guest_state) {
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 3a7630fdd340..d20e4f8d1aef 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2761,11 +2761,10 @@ static bool perf_hw_regs(struct pt_regs *regs)
>   void
>   perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct unwind_state state;
>   	unsigned long addr;
>   
> -	if (guest_cbs && guest_cbs->state()) {
> +	if (perf_guest_state()) {
>   		/* TODO: We don't support guest os callchain now */
>   		return;
>   	}
> @@ -2865,11 +2864,10 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
>   void
>   perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
>   	struct stack_frame frame;
>   	const struct stack_frame __user *fp;
>   
> -	if (guest_cbs && guest_cbs->state()) {
> +	if (perf_guest_state()) {
>   		/* TODO: We don't support guest os callchain now */
>   		return;
>   	}
> @@ -2946,18 +2944,15 @@ static unsigned long code_segment_base(struct pt_regs *regs)
>   
>   unsigned long perf_instruction_pointer(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -
> -	if (guest_cbs && guest_cbs->state())
> -		return guest_cbs->get_ip();
> +	if (perf_guest_state())
> +		return perf_guest_get_ip();
>   
>   	return regs->ip + code_segment_base(regs);
>   }
>   
>   unsigned long perf_misc_flags(struct pt_regs *regs)
>   {
> -	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> -	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
> +	unsigned int guest_state = perf_guest_state();
>   	int misc = 0;
>   
>   	if (guest_state) {
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 524ad1f747bd..f5b02017ba16 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2786,7 +2786,6 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>   {
>   	struct perf_sample_data data;
>   	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> -	struct perf_guest_info_callbacks *guest_cbs;
>   	int bit;
>   	int handled = 0;
>   	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
> @@ -2853,9 +2852,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>   	 */
>   	if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
>   		handled++;
> -
> -		guest_cbs = perf_get_guest_cbs();
> -		if (likely(!guest_cbs || !guest_cbs->handle_intel_pt_intr()))
> +		if (!perf_guest_handle_intel_pt_intr())
>   			intel_pt_interrupt();
>   	}
>   
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f9be88a47434..c0a6eaf55fb1 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1247,6 +1247,30 @@ static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
>   	/* Prevent reloading between a !NULL check and dereferences. */
>   	return READ_ONCE(perf_guest_cbs);
>   }
> +static inline unsigned int perf_guest_state(void)
> +{
> +	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> +
> +	return guest_cbs ? guest_cbs->state() : 0;
> +}
> +static inline unsigned long perf_guest_get_ip(void)
> +{
> +	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> +
> +	/*
> +	 * Arbitrarily return '0' in the unlikely scenario that the callbacks
> +	 * are unregistered between checking guest state and getting the IP.
> +	 */
> +	return guest_cbs ? guest_cbs->get_ip() : 0;
> +}
> +static inline unsigned int perf_guest_handle_intel_pt_intr(void)
> +{
> +	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
> +
> +	if (guest_cbs && guest_cbs->handle_intel_pt_intr)
> +		return guest_cbs->handle_intel_pt_intr();
> +	return 0;
> +}
>   extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
>   extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
>   
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>