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

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Message-ID: <aCxOKIGgcxDlg+Fn@yzhao56-desk.sh.intel.com>
Date: Tue, 20 May 2025 17:40:56 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<rick.p.edgecombe@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...el.com>, <tabba@...gle.com>, <ackerleytng@...gle.com>,
	<quic_eberman@...cinc.com>, <michael.roth@....com>, <david@...hat.com>,
	<vannapurve@...gle.com>, <vbabka@...e.cz>, <jroedel@...e.de>,
	<thomas.lendacky@....com>, <pgonda@...gle.com>, <zhiquan1.li@...el.com>,
	<fan.du@...el.com>, <jun.miao@...el.com>, <ira.weiny@...el.com>,
	<isaku.yamahata@...el.com>, <xiaoyao.li@...el.com>, <chao.p.peng@...el.com>
Subject: Re: [RFC PATCH 14/21] KVM: x86/tdp_mmu: Invoke split_external_spt
 hook with exclusive mmu_lock

On Tue, May 20, 2025 at 01:40:46PM +0800, Binbin Wu wrote:
> 
> 
> On 4/24/2025 11:07 AM, 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);
> Better to use kvm_x86_call() instead of static_call().
Will do. Thanks!

> > +	KVM_BUG_ON(ret, kvm);
> > +
> > +	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);
> >   	}
> >   	return old_spte;
>