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

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Message-ID: <20210810143716.daz5p3mf5bbeyp74@linux.intel.com>
Date:   Tue, 10 Aug 2021 22:37:16 +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 02:47:27PM +0200, Paolo Bonzini wrote:
> 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.

Interesting. :) Thanks a lot for the explanation!

B.R.
Yu