linux-kernel - Re: [PATCH 14/21] KVM: TDX: Implement hooks to propagate changes of TDP MMU mirror page table

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Message-ID: <4b2bea4b62445db76b5ac5c6083a72ffffd8f5d0.camel@intel.com>
Date: Tue, 10 Sep 2024 23:58:01 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>
CC: "nik.borisov@...e.com" <nik.borisov@...e.com>, "dmatlack@...gle.com"
	<dmatlack@...gle.com>, "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/21] KVM: TDX: Implement hooks to propagate changes of
 TDP MMU mirror page table

On Tue, 2024-09-10 at 11:33 +0200, Paolo Bonzini wrote:
> > But actually, I wonder if we need to remove the KVM_BUG_ON(). I think if you
> > did
> > a KVM_PRE_FAULT_MEMORY and then deleted the memslot you could hit it?
> 
> I think all paths to handle_removed_pt() are safe:
> 
> __tdp_mmu_zap_root
>          tdp_mmu_zap_root
>                  kvm_tdp_mmu_zap_all
>                          kvm_arch_flush_shadow_all
>                                  kvm_flush_shadow_all
>                                          kvm_destroy_vm (*)
>                                          kvm_mmu_notifier_release (*)
>                  kvm_tdp_mmu_zap_invalidated_roots
>                          kvm_mmu_zap_all_fast (**)
> kvm_tdp_mmu_zap_sp
>          kvm_recover_nx_huge_pages (***)

But not all paths to remove_external_spte():
kvm_arch_flush_shadow_memslot()
  kvm_mmu_zap_memslot_leafs()
    kvm_tdp_mmu_unmap_gfn_range()
      tdp_mmu_zap_leafs()
        tdp_mmu_iter_set_spte()
          tdp_mmu_set_spte()
            remove_external_spte()
              tdx_sept_remove_private_spte()

But we can probably keep the warning if we prevent KVM_PRE_FAULT_MEMORY as you
pointed earlier. I didn't see that that kvm->arch.pre_fault_allowed  got added.