Re: [PATCH 09/21] KVM: TDX: Retry seamcall when TDX_OPERAND_BUSY with operand SEPT

[Huang, Kai]

On Thu, 2024-10-10 at 21:53 +0000, Edgecombe, Rick P wrote:
> On Thu, 2024-10-10 at 10:33 -0700, Sean Christopherson wrote:
> > > 
> > > 1st: "fault->is_private != kvm_mem_is_private(kvm, fault->gfn)" is found.
> > > 2nd-6th: try_cmpxchg64() fails on each level SPTEs (5 levels in total)
> 
> Isn't there a more general scenario:
> 
> vcpu0                              vcpu1
> 1. Freezes PTE
> 2. External op to do the SEAMCALL
> 3.                                 Faults same PTE, hits frozen PTE
> 4.                                 Retries N times, triggers zero-step
> 5. Finally finishes external op
> 
> Am I missing something?

I must be missing something.  I thought KVM is going to retry internally for
step 4 (retries N times) because it sees the frozen PTE, but will never go back
to guest after the fault is resolved?  How can step 4 triggers zero-step?