Re: [PATCH 0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups

[Paolo Bonzini <pbonzini@redhat.com>]

On 2/25/25 00:55, Sean Christopherson wrote:
> This was _supposed_ to be a tiny one-off patch to fix a nVMX bug where KVM
> fails to detect that, after nested VM-Exit, L1 has a pending IRQ (or NMI).
> But because x86's nested teardown flows are garbage (KVM simply forces a
> nested VM-Exit to put the vCPU back into L1), that simple fix snowballed.
> 
> The immediate issue is that checking for a pending interrupt accesses the
> legacy PIC, and x86's kvm_arch_destroy_vm() currently frees the PIC before
> destroying vCPUs, i.e. checking for IRQs during the forced nested VM-Exit
> results in a NULL pointer deref (or use-after-free if KVM didn't nullify
> the PIC pointer).  That's patch 1.
> 
> Patch 2 is the original nVMX fix.
> 
> The remaining patches attempt to bring a bit of sanity to x86's VM
> teardown code, which has accumulated a lot of cruft over the years.  E.g.
> KVM currently unloads each vCPU's MMUs in a separate operation from
> destroying vCPUs, all because when guest SMP support was added, KVM had a
> kludgy MMU teardown flow that broken when a VM had more than one 1 vCPU.
> And that oddity lived on, for 18 years...

Queued patches 1 and 2 to kvm/master, and everything to kvm/queue 
(pending a little more testing and the related TDX change).

Paolo