Re: [REGRESSION] KVM: x86: OVMF boot hang with SMM enabled after commit b3e6212dea2e ("KVM: x86: Use active memslots for the per-vCPU MMIO cache")

[Paolo Bonzini]

On 10/28/26 18:37, Sean Christopherson wrote:
> > However, address space 0 and address space 1 maintain separate 
generation counters
> > starting from 0.

This is also incorrect:

        for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
                for (j = 0; j < 2; j++) {
                        slots = &kvm->__memslots[i][j];

                        atomic_long_set(&slots->last_used_slot, 
(unsigned long)NULL);
                        slots->hva_tree = RB_ROOT_CACHED;
                        slots->gfn_tree = RB_ROOT;
                        hash_init(slots->id_hash);
                        slots->node_idx = j;

                        /* Generations must be different for each 
address space. */
                        slots->generation = i;
                }


> >          An MMIO access cached in SMM (e.g., GFN 0xFED40000 with gen = 4) matches in normal mode where gen is also 4.
> Hmm, this isn't adding up for me.  It should be impossible for the generation to
> be '4' for SMM, because SMM is supposed to use odd-numbered generations.  From
> kvm_swap_active_memslots():

vcpu_cache_mmio_info() does not use the address space id:

        u64 gen = kvm_memslots(vcpu->kvm)->generation;

Will send a patch soon.

Paolo