linux-kernel - Re: [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP level

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Message-ID: <998dca9a-84b6-20ee-2646-3eb58df0b8a0@redhat.com>
Date:   Tue, 10 Aug 2021 14:47:27 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.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 10/08/21 13:00, Yu Zhang wrote:
> 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...

Yes, on Linux that will be one of 3/4/5 based on host paging mode, and 
it will apply to all N_CR3...

> But shadow EPT does not have such annoyance. Is above understanding correct?

... Right, because shadow EPT cannot have less than 4 levels, and it can 
always use 4 levels if that's what L1 uses.

Paolo