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

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