Re: [RFC PATCH 09/12] KVM: TDX: Fold tdx_mem_page_record_premap_cnt() into its sole caller

[Binbin Wu]

On 8/29/2025 2:52 AM, Edgecombe, Rick P wrote:
> On Thu, 2025-08-28 at 10:00 -0700, Sean Christopherson wrote:
> > On Thu, Aug 28, 2025, Yan Zhao wrote:
[...]
> > > 3. Unexpected zaps (such as kvm_zap_gfn_range()).
> > Side topic related to kvm_zap_gfn_range(), the KVM_BUG_ON() in vt_refresh_apicv_exec_ctrl()
> > is flawed.  If kvm_recalculate_apic_map() fails to allocate an optimized map, KVM
> > will mark APICv as inhibited, i.e. the associated WARN_ON_ONCE() is effectively
> > user-triggerable.
> >
> > Easiest thing would be to mark the vCPU as dead (though we obviously need
> > "KVM: Never clear KVM_REQ_VM_DEAD from a vCPU's requests" for that to be robust).
> I'm going need to look up the related apic discussions from the base series and
> circle back.
There was an analysis about the inhibit reasons for TDX.
https://lore.kernel.org/lkml/e3a2e8fa-b496-4010-9a8c-bfeb131bc43b@xxxxxxxxxxxxxxx/

As Sean mentioned, if kvm_recalculate_apic_map() fails to allocate the memory
for optimized map, it will trigger the KVM_BUG_ON() in
vt_refresh_apicv_exec_ctrl(). And kvzalloc() failure should not be treated as
KVM bug.

As talking about user-triggerable, the kvzalloc() failure path could be
triggered by KVM_CREATE_VCPU and KVM_TDX_INIT_VCPU for TD. After
KVM_TDX_INIT_VCPU, the mapping is not allowed to be changed.

Sean's suggested code change looks good to me.