On Fri, Feb 18, 2022, Paolo Bonzini wrote:
> 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.
Agreed, I bet similar warnings can be triggered on SVM with nrips=false due to
svm_skip_emulated_instruction() dropping into the emulator, e.g. for HyperV and
Xen usage where next_rip doesn't appear to be filled in all paths.
