On Wed, 18 Oct 2023 13:46:21 -0700, Sean Christopherson wrote:
> Clean up a KVM module refcounting mess that Al pointed out in the context
> of the guest_memfd series. The worst behavior was recently introduced by
> an ill-fated attempt to fix a bug in x86's async #PF code. Instead of
> fixing the underlying bug of not flushing a workqueue (see patch 2), KVM
> fudged around the bug by gifting every VM a reference to the KVM module.
>
> That made the reproducer happy (hopefully there was actually a reproducer
> at one point), but it didn't fully fix the use-after-free bug, it just made
> the bug harder to hit. E.g. as pointed out by Al, if kvm_destroy_vm() is
> preempted after putting the last KVM module reference, KVM can be unloaded
> before kvm_destroy_vm() completes, and scheduling back in the associated
> task will explode (preemption isn't strictly required, it's just the most
> obvious path to failure).
>
> [...]
Applied 1 and 3 (the .owner fixes) to kvm-x86 fixes. I'll follow-up with a
separate series to tackle the async #PF mess.
[1/3] KVM: Set file_operations.owner appropriately for all such structures
https://github.com/kvm-x86/linux/commit/087e15206d6a
[2/3] KVM: Always flush async #PF workqueue when vCPU is being destroyed
(no commit info)
[3/3] Revert "KVM: Prevent module exit until all VMs are freed"
https://github.com/kvm-x86/linux/commit/ea61294befd3
--
https://github.com/kvm-x86/linux/tree/next
