linux-kernel - Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for kvm_tdp_mmu_invalidate_all

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Date: Tue, 25 Jun 2024 14:14:30 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for
 kvm_tdp_mmu_invalidate_all_roots()

On Tue, Jun 25, 2024 at 07:15:09AM +0800, Edgecombe, Rick P wrote:
> On Mon, 2024-06-24 at 16:29 +0800, Yan Zhao wrote:
> > > @@ -1057,7 +1057,7 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm)
> > >           * KVM_RUN is unreachable, i.e. no vCPUs will ever service the
> > > request.
> > >           */
> > >          lockdep_assert_held_write(&kvm->mmu_lock);
> > > -       for_each_tdp_mmu_root_yield_safe(kvm, root)
> > > +       __for_each_tdp_mmu_root_yield_safe(kvm, root, -1, KVM_DIRECT_ROOTS)
> > nit: update the comment of kvm_tdp_mmu_zap_all() 
> 
> Yea, good idea. It's definitely needs some explanation, considering the function
> is called "zap_all". A bit unfortunate actually.
> 
> > and explain why it's
> > KVM_DIRECT_ROOTS, not KVM_DIRECT_ROOTS | KVM_INVALID_ROOTS.
> 
> Explain why not to zap invalid mirrored roots?
No. Explain why not to zap invalid direct roots.
Just passing KVM_DIRECT_ROOTS will zap only valid direct roots, right?
The original kvm_tdp_mmu_zap_all() "Zap all roots, including invalid roots".
It might be better to explain why not to zap invalid direct roots here.