Commit 176cda0619 ("powerpc/perf: Add perf interface to expose vpa
counters") introduced 'vpa_pmu' to expose Book3s-HV nested APIv2 provided
L1<->L2 context switch latency counters to L1 user-space via
perf-events. However the newly introduced PMU named 'vpa_pmu' doesn't
assign ownership of the PMU to the module 'vpa_pmu'. Consequently the
module 'vpa_pmu' can be unloaded while one of the perf-events are still
active, which can lead to kernel oops and panic of the form below on a
Pseries-LPAR:
BUG: Kernel NULL pointer dereference on read at 0x00000058
<snip>
NIP [c000000000506cb8] event_sched_out+0x40/0x258
LR [c00000000050e8a4] __perf_remove_from_context+0x7c/0x2b0
Call Trace:
[c00000025fc3fc30] [c00000025f8457a8] 0xc00000025f8457a8 (unreliable)
[c00000025fc3fc80] [fffffffffffffee0] 0xfffffffffffffee0
[c00000025fc3fcd0] [c000000000501e70] event_function+0xa8/0x120
<snip>
Kernel panic - not syncing: Aiee, killing interrupt handler!
Fix this by adding the module ownership to 'vpa_pmu' so that the module
'vpa_pmu' is ref-counted and prevented from being unloaded when perf-events
are initialized.
Fixes: 176cda0619 ("powerpc/perf: Add perf interface to expose vpa counters")
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250204153527.125491-1-vaibhav@linux.ibm.com
Enhance the vpa_pmu driver with a feature to observe context switch
latency event for both per-task (tid) and per-pid (pid) option.
Couple of new helper functions are added to hide the abstraction of
reading the context switch latency counter from kvm_vcpu_arch struct
and these helper functions are defined in the "kvm/book3s_hv.c".
"PERF_ATTACH_TASK" flag is used to decide whether to read the counter
values from lppaca or kvm_vcpu_arch struct.
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Co-developed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241118114114.208964-4-kjain@linux.ibm.com
To support performance measurement for KVM on PowerVM(KoP)
feature, PowerVM hypervisor has added couple of new software
counters in Virtual Process Area(VPA) of the partition.
Commit e1f288d2f9 ("KVM: PPC: Book3S HV nestedv2: Add
support for reading VPA counters for pseries guests")
have updated the paca fields with corresponding changes.
Proposed perf interface is to expose these new software
counters for monitoring of context switch latencies and
runtime aggregate. Perf interface driver is called
"vpa_pmu" and it has dependency on KVM and perf, hence
added new config called "VPA_PMU" which depends on
"CONFIG_KVM_BOOK3S_64_HV" and "CONFIG_HV_PERF_CTRS".
Since, kvm and kvm_host are currently compiled as built-in
modules, this perf interface takes the same path and
registered as a module.
vpa_pmu perf interface needs access to some of the kvm
functions and structures like kvmhv_get_l2_counters_status(),
hence kvm_book3s_64.h and kvm_ppc.h are included.
Below are the events added to monitor KoP:
vpa_pmu/l1_to_l2_lat/
vpa_pmu/l2_to_l1_lat/
vpa_pmu/l2_runtime_agg/
and vpa_pmu driver supports only per-cpu monitoring with this patch.
Example usage:
[command]# perf stat -e vpa_pmu/l1_to_l2_lat/ -a -I 1000
1.001017682 727,200 vpa_pmu/l1_to_l2_lat/
2.003540491 1,118,824 vpa_pmu/l1_to_l2_lat/
3.005699458 1,919,726 vpa_pmu/l1_to_l2_lat/
4.007827011 2,364,630 vpa_pmu/l1_to_l2_lat/
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Co-developed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241118114114.208964-1-kjain@linux.ibm.com
