Re: [PATCH 14/17] KVM: x86/mmu: Remove KVM_BUG_ON() that checks lock when removing PTs

[Yan Zhao]

On Fri, Mar 27, 2026 at 01:14:18PM -0700, Rick Edgecombe wrote:
> As part of an ongoing effort to move TDX specific bits from the MMU into
> the TDX code, drop the KVM_BUG_ON() that checks the MMU lock is held for
> write while removing page tables.
> 
> Future changes forward PTE removal mirror EPT updates into the
> set_private_spte() and let TDX code parse the PTE to decide what S-EPT
> operations to take. This operations does not pass a shared bool for this
"operations" --> "operation" ?

> KVM_BUG_ON() to use in the logics future home.
By "in the logics future home", do you mean "when this logic is moved to its
future location"?
 
> But even today there are already MMU write lockdep asserts that mostly
> cover the case. Since the KVM_BUG_ON() is already a bit redundant, just
> remove it instead of trying to plumb the bool into TDX code.
> 
> Link: https://lore.kernel.org/kvm/aYUarHf3KEwHGuJe@xxxxxxxxxx/
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 991870789863..5dc9633c866e 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -473,10 +473,8 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
>  		}
>  		handle_changed_spte(kvm, sp, gfn, old_spte, FROZEN_SPTE, level, shared);
>  
> -		if (is_mirror_sp(sp)) {
> -			KVM_BUG_ON(shared, kvm);
> +		if (is_mirror_sp(sp))
>  			remove_external_spte(kvm, gfn, old_spte, level);
> -		}
>  	}
>  
>  	if (is_mirror_sp(sp) &&
> -- 
> 2.53.0
>