Messages in this thread | | | Date | Fri, 18 Feb 2022 12:20:08 +0100 | Subject | Re: [PATCH 2/2] KVM: x86/pmu: Protect kvm->arch.pmu_event_filter with SRCU | From | Paolo Bonzini <> |
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On 2/17/22 09:36, Like Xu wrote: > From: Like Xu<likexu@tencent.com> > > 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.
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