On 2/17/22 09:36, Like Xu wrote:
From: Like Xu<likexu@xxxxxxxxxxx>
Fix the following positive warning:
=============================
WARNING: suspicious RCU usage
arch/x86/kvm/pmu.c:190 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by CPU 28/KVM/370841:
#0: ff11004089f280b8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x87/0x730 [kvm]
Call Trace:
<TASK>
dump_stack_lvl+0x59/0x73
reprogram_fixed_counter+0x15d/0x1a0 [kvm]
kvm_pmu_trigger_event+0x1a3/0x260 [kvm]
? free_moved_vector+0x1b4/0x1e0
complete_fast_pio_in+0x8a/0xd0 [kvm]
[...]
I think the right fix is to add SRCU protection to complete_userspace_io
in kvm_arch_vcpu_ioctl_run. Most calls of complete_userspace_io can
execute similar code to vmexits.
Fixes: 66bb8a065f5a ("KVM: x86: PMU Event Filter")
It fixes 9cd803d496e7 ("KVM: x86: Update vPMCs when retiring
instructions", 2022-01-07), actually. That is when the PMU filter was
added to kvm_skip_emulated_instruction (called by kvm_fast_pio_in).
Thanks,
Paolo
It's possible to call KVM_SET_PMU_EVENT_FILTER ioctl with the vCPU running.
Similar to "kvm->arch.msr_filter", KVM should guarantee that vCPUs will
see either the previous filter or the new filter so that guest pmu events
with identical settings in both the old and new filter have deterministic
behavior.
