linux-kernel - Re: [RFC PATCH v5 05/45] KVM: TDX: Drop kvm_x86_ops.link_external_spt(), use .set_external

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aYUkVRedz9ngwu_1@google.com>
Date: Thu, 5 Feb 2026 15:14:29 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Kiryl Shutsemau <kas@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, 
	linux-coco@...ts.linux.dev, kvm@...r.kernel.org, 
	Kai Huang <kai.huang@...el.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Vishal Annapurve <vannapurve@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>, 
	Sagi Shahar <sagis@...gle.com>, Binbin Wu <binbin.wu@...ux.intel.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [RFC PATCH v5 05/45] KVM: TDX: Drop kvm_x86_ops.link_external_spt(),
 use .set_external_spte() for all

On Wed, Feb 04, 2026, Yan Zhao wrote:
> On Tue, Feb 03, 2026 at 08:05:05PM +0000, Sean Christopherson wrote:
> > On Tue, Feb 03, 2026, Yan Zhao wrote:
> > > On Wed, Jan 28, 2026 at 05:14:37PM -0800, Sean Christopherson wrote:
> > > >  static int __must_check set_external_spte_present(struct kvm *kvm, tdp_ptep_t sptep,
> > > >  						 gfn_t gfn, u64 *old_spte,
> > > >  						 u64 new_spte, int level)
> > > >  {
> > > > -	bool was_present = is_shadow_present_pte(*old_spte);
> > > > -	bool is_present = is_shadow_present_pte(new_spte);
> > > > -	bool is_leaf = is_present && is_last_spte(new_spte, level);
> > > > -	int ret = 0;
> > > > -
> > > > -	KVM_BUG_ON(was_present, kvm);
> > > > +	int ret;
> > > >  
> > > >  	lockdep_assert_held(&kvm->mmu_lock);
> > > > +
> > > > +	if (KVM_BUG_ON(is_shadow_present_pte(*old_spte), kvm))
> > > > +		return -EIO;
> > > Why not move this check of is_shadow_present_pte() to tdx_sept_set_private_spte()
> > > as well? 
> > 
> > The series gets there eventually, but as of this commit, @old_spte isn't plumbed
> > into tdx_sept_set_private_spte().
> > 
> > > Or also check !is_shadow_present_pte(new_spte) in TDP MMU?
> > 
> > Not sure I understand this suggestion.
> Sorry. The accurate expression should be 
> "what about moving !is_shadow_present_pte(new_spte) to TDP MMU as well?".

It's already there, in __tdp_mmu_set_spte_atomic():

		/*
		 * KVM doesn't currently support zapping or splitting mirror
		 * SPTEs while holding mmu_lock for read.
		 */
		if (KVM_BUG_ON(is_shadow_present_pte(iter->old_spte), kvm) ||
		    KVM_BUG_ON(!is_shadow_present_pte(new_spte), kvm))
			return -EBUSY;


> > > And as Rick also mentioned, better to remove external in external_spt, e.g.
> > > something like pt_page.
> > 
> > Yeah, maybe sept_spt?
> Hmm, here sept_spt is of type struct page, while sp->spt and sp->external_spt
> represents VA. Not sure if it will cause confusion.

How about sept_pt?