linux-kernel - Re: [RFC PATCH 14/21] KVM: x86/tdp_mmu: Invoke split_external_spt hook with exclusive mmu

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: <aCcCl6nSvYpSK1A2@yzhao56-desk.sh.intel.com>
Date: Fri, 16 May 2025 17:17:11 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Shutemov, Kirill" <kirill.shutemov@...el.com>,
	"quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen,
 Dave" <dave.hansen@...el.com>, "david@...hat.com" <david@...hat.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "tabba@...gle.com"
	<tabba@...gle.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>, "Du, Fan"
	<fan.du@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "michael.roth@....com"
	<michael.roth@....com>, "Weiny, Ira" <ira.weiny@...el.com>, "vbabka@...e.cz"
	<vbabka@...e.cz>, "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "Peng, Chao P" <chao.p.peng@...el.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "jroedel@...e.de"
	<jroedel@...e.de>, "Miao, Jun" <jun.miao@...el.com>, "pgonda@...gle.com"
	<pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 14/21] KVM: x86/tdp_mmu: Invoke split_external_spt
 hook with exclusive mmu_lock

On Wed, May 14, 2025 at 07:06:48AM +0800, Edgecombe, Rick P wrote:
> On Thu, 2025-04-24 at 11:07 +0800, Yan Zhao wrote:
> > +static int split_external_spt(struct kvm *kvm, gfn_t gfn, u64 old_spte,
> > +			      u64 new_spte, int level)
> > +{
> > +	void *external_spt = get_external_spt(gfn, new_spte, level);
> > +	int ret;
> > +
> > +	KVM_BUG_ON(!external_spt, kvm);
> > +
> > +	ret = static_call(kvm_x86_split_external_spt)(kvm, gfn, level, external_spt);
> > +	KVM_BUG_ON(ret, kvm);
> 
> 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?

> > +	return ret;
> > +}
> >  /**
> >   * handle_removed_pt() - handle a page table removed from the TDP structure
> >   *
> > @@ -764,13 +778,13 @@ static u64 tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,
> >  
> >  	handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);
> >  
> > -	/*
> > -	 * Users that do non-atomic setting of PTEs don't operate on mirror
> > -	 * roots, so don't handle it and bug the VM if it's seen.
> > -	 */
> >  	if (is_mirror_sptep(sptep)) {
> > -		KVM_BUG_ON(is_shadow_present_pte(new_spte), kvm);
> > -		remove_external_spte(kvm, gfn, old_spte, level);
> > +		if (!is_shadow_present_pte(new_spte))
> > +			remove_external_spte(kvm, gfn, old_spte, level);
> > +		else if (is_last_spte(old_spte, level) && !is_last_spte(new_spte, level))
> > +			split_external_spt(kvm, gfn, old_spte, new_spte, level);
> > +		else
> > +			KVM_BUG_ON(1, kvm);
> 
> It might be worth a comment what this is looking for at this point. I think it's
> that external EPT only support certain operations, so bug if any unsupported
> operations are seen.
Will do.

> >  	}
> >  
> >  	return old_spte;
>