Message ID | 20240911222433.3415301-6-coltonlewis@google.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | Correct perf sampling with Guest VMs | expand |
On Wed, Sep 11, 2024, Colton Lewis wrote: > 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 clear. This way any host-only events with exclude_guest > set will never see unexpected guest samples. The behaviour of events > with exclude_guest clear is unchanged. Nit, "with exclude_guest clear" is easy to misread as simply "with exclude_guest" (I did so at least three times). Maybe The behavior of exclude_guest=0 events is unchanged. or The behavior of events without exclude_guest is unchanged. I think it's also worth explicitly calling out that events that are configured to sample both host and guest may still be prone to misattributing a PMI that arrived in the host as a guest event, depending on the KVM arch and/or vendor behavior.
Hi Colton,
kernel test robot noticed the following build warnings:
[auto build test WARNING on perf-tools-next/perf-tools-next]
[also build test WARNING on tip/perf/core perf-tools/perf-tools acme/perf/core linus/master v6.11-rc7 next-20240912]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Colton-Lewis/arm-perf-Drop-unused-functions/20240912-063910
base: https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git perf-tools-next
patch link: https://lore.kernel.org/r/20240911222433.3415301-6-coltonlewis%40google.com
patch subject: [PATCH v2 5/5] perf: Correct perf sampling with guest VMs
config: x86_64-buildonly-randconfig-005-20240912 (https://download.01.org/0day-ci/archive/20240912/202409122254.PnIe8ulL-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240912/202409122254.PnIe8ulL-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409122254.PnIe8ulL-lkp@intel.com/
All warnings (new ones prefixed by >>):
arch/x86/events/core.c: In function 'perf_arch_misc_flags':
>> arch/x86/events/core.c:2971:22: warning: unused variable 'guest_state' [-Wunused-variable]
2971 | unsigned int guest_state = perf_guest_state();
| ^~~~~~~~~~~
vim +/guest_state +2971 arch/x86/events/core.c
8f19518b57cef1 arch/x86/events/core.c Colton Lewis 2024-09-11 2968
a2d1490e40282f arch/x86/events/core.c Colton Lewis 2024-09-11 2969 unsigned long perf_arch_misc_flags(struct pt_regs *regs)
39447b386c846b arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-19 2970 {
1c3430516b0732 arch/x86/events/core.c Sean Christopherson 2021-11-11 @2971 unsigned int guest_state = perf_guest_state();
8f19518b57cef1 arch/x86/events/core.c Colton Lewis 2024-09-11 2972 unsigned long misc = common_misc_flags(regs);
dcf46b9443ad48 arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-20 2973
d07bdfd322d307 arch/x86/kernel/cpu/perf_event.c Peter Zijlstra 2012-07-10 2974 if (user_mode(regs))
dcf46b9443ad48 arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-20 2975 misc |= PERF_RECORD_MISC_USER;
dcf46b9443ad48 arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-20 2976 else
dcf46b9443ad48 arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-20 2977 misc |= PERF_RECORD_MISC_KERNEL;
dcf46b9443ad48 arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-20 2978
39447b386c846b arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-19 2979 return misc;
39447b386c846b arch/x86/kernel/cpu/perf_event.c Zhang, Yanmin 2010-04-19 2980 }
b3d9468a8bd218 arch/x86/kernel/cpu/perf_event.c Gleb Natapov 2011-11-10 2981
diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h index 31a5584ed423..ee45b4e77347 100644 --- a/arch/arm64/include/asm/perf_event.h +++ b/arch/arm64/include/asm/perf_event.h @@ -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) ®s->user_regs #endif diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c index 01a9d08fc009..9b7f26b128b5 100644 --- a/arch/arm64/kernel/perf_callchain.c +++ b/arch/arm64/kernel/perf_callchain.c @@ -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; -} diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index d51e5d24802b..5f119b9516dc 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2942,9 +2942,6 @@ 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); } @@ -2974,14 +2971,10 @@ unsigned long perf_arch_misc_flags(struct pt_regs *regs) unsigned int guest_state = perf_guest_state(); unsigned long misc = common_misc_flags(regs); - if (guest_state) { - misc |= perf_arch_guest_misc_flags(regs); - } else { - if (user_mode(regs)) - misc |= PERF_RECORD_MISC_USER; - else - misc |= PERF_RECORD_MISC_KERNEL; - } + if (user_mode(regs)) + misc |= PERF_RECORD_MISC_USER; + else + misc |= PERF_RECORD_MISC_KERNEL; return misc; } diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index d061e327ad54..968f3edd95e4 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1633,8 +1633,9 @@ 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) \ @@ -1645,6 +1646,22 @@ 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_USER) + return PERF_RECORD_MISC_GUEST_USER; + + if (guest_state & PERF_GUEST_ACTIVE) + return PERF_RECORD_MISC_GUEST_KERNEL; + + return 0; +} +# 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; diff --git a/kernel/events/core.c b/kernel/events/core.c index eeabbf791a8c..c5e57c024d9a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6921,13 +6921,26 @@ 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); } @@ -7743,7 +7756,7 @@ 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; } @@ -7907,7 +7920,7 @@ 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
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 clear. This way any host-only events with exclude_guest set will never see unexpected guest samples. The behaviour of events with exclude_guest clear is unchanged. Signed-off-by: Colton Lewis <coltonlewis@google.com> --- arch/arm64/include/asm/perf_event.h | 4 ---- arch/arm64/kernel/perf_callchain.c | 28 ---------------------------- arch/x86/events/core.c | 15 ++++----------- include/linux/perf_event.h | 21 +++++++++++++++++++-- kernel/events/core.c | 21 +++++++++++++++++---- 5 files changed, 40 insertions(+), 49 deletions(-)