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Date: Tue, 10 Aug 2021 19:00:31 +0800 From: Yu Zhang <yu.c.zhang@...ux.intel.com> To: Paolo Bonzini <pbonzini@...hat.com> Cc: Sean Christopherson <seanjc@...gle.com>, Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com Subject: Re: [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP level On Tue, Aug 10, 2021 at 11:25:27AM +0200, Paolo Bonzini wrote: > On 10/08/21 09:40, Yu Zhang wrote: > > About "host can't easily mirror L1's desired paging mode", could you please elaborate? > > Thanks! > > Shadow pgae tables in KVM will always have 3 levels on 32-bit machines and > 4/5 levels on 64-bit machines. L1 instead might have any number of levels > from 2 to 5 (though of course not more than the host has). Thanks Paolo. I guess it's because, unlike EPT which are with either 4 or 5 levels, NPT's level can range from 2 to 5, depending on the host paging mode... > > Therefore, when shadowing 32-bit NPT page tables, KVM has to add extra fixed > levels on top of those that it's shadowing. See mmu_alloc_direct_roots for > the code. So when shadowing NPTs(can be 2/3 levels, depending on the paging mode in L1), and if L0 Linux is running in 4/5 level mode, extra levels of paging structures is needed in the shadow NPT. But shadow EPT does not have such annoyance. Is above understanding correct? B.R. Yu
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