Re: [RFC PATCH 14/21] KVM: x86/tdp_mmu: Invoke split_external_spt hook with exclusive mmu_lock

[Yan Zhao]

On Sat, May 17, 2025 at 06:11:59AM +0800, Edgecombe, Rick P wrote:
> On Fri, 2025-05-16 at 17:17 +0800, Yan Zhao wrote:
> > > Shouldn't this BUG_ON be handled in the split_external_spt implementation? I
> > > don't think we need another one.
> > Ok. But kvm_x86_split_external_spt() is not for TDX only.
> > Is it good for KVM MMU core to rely on each implementation to trigger BUG_ON?
> 
> It effectively is for TDX only. At least for the foreseeable future. The naming
> basically means that people don't have to see "TDX" everywhere when they look in
> the MMU code.
Hmm, another reason to add the BUG_ON is to align it with remove_external_spte().
There's also a KVM_BUG_ON() following the remove_external_spte hook.

I interpret this as error handling in the KVM MMU core, which returns "void",
so issuing BUG_ON if ret != 0.