Re: [PATCH v2] KVM: x86: Handle SRCU initialization failure during page track init

[Paolo Bonzini]

On 03/09/21 18:18, Sean Christopherson wrote:
> Before moving forward with a fix, I'd like to get Paolo's input on dropping
> track_srcu in favor of kvm->srcu and avoiding this altogheter.  Note, Paolo is on
> vacation at the moment, so this won't get attention for a week or more.

The reason for track_srcu's existence is to avoid complications in 
kvm_arch_flush_shadow_memslot, which is called from the _write_ side of 
kvm->srcu but is on the _read_ side of track_srcu.

I think this should be fixed easily by taking slots_lock in 
kvm_page_track_register_notifier and kvm_page_track_unregister_notifier, 
however it's a bit more complicated from the point of view of the lock 
hierarchy and possible deadlocks.

So I'm open to patches that drop track_srcu, but for now I applied this 
patch.

Paolo