Re: [PATCH] KVM: x86: use again the flush argument of __link_shadow_page()

[Sean Christopherson <seanjc@google.com>]

x86/mmu

On Sun, May 03, 2026, Paolo Bonzini wrote:
> Except in the case of parentless nested-TDP pages, mmu_page_zap_pte()
> clears the SPTE but leaves the invalid_list empty.  In this case, using
> kvm_flush_remote_tlbs() as kvm_mmu_remote_flush_or_zap() does is overkill.
> Avoid flushing the entirety of the remote TLBs unless the invalid_list
> was populated: instead, use a more efficient gfn-targeting flush (if
> available) and skip it altogether if the caller guarantees that a TLB
> flush is not necessary.
> 
> Based-on: <20260503201029.106481-1-pbonzini@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 892246204435..85bec8eeace8 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2541,8 +2541,10 @@ static void __link_shadow_page(struct kvm *kvm,
>  		parent_sp = sptep_to_sp(sptep);
>  		WARN_ON_ONCE(parent_sp->role.level == PG_LEVEL_4K);
>  
> -		mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list);
> -		kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, true);
> +		if (mmu_page_zap_pte(kvm, parent_sp, sptep, &invalid_list))
> +			kvm_mmu_commit_zap_page(kvm, &invalid_list);
> +		else if (flush)
> +			kvm_flush_remote_tlbs_sptep(kvm, sptep);

Duh, this is obvious in hindsight.

Reviewed-by: Sean Christopherson <seanjc@google.com>