Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP
 level
To:     Yu Zhang <yu.c.zhang@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     Wei Huang <wei.huang2@amd.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, vkuznets@redhat.com,
        wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        hpa@zytor.com
References: <20210808192658.2923641-1-wei.huang2@amd.com>
 <20210808192658.2923641-2-wei.huang2@amd.com>
 <20210809035806.5cqdqm5vkexvngda@linux.intel.com>
 <c6324362-1439-ef94-789b-5934c0e1cdb8@amd.com>
 <20210809042703.25gfuuvujicc3vj7@linux.intel.com>
 <73bbaac0-701c-42dd-36da-aae1fed7f1a0@amd.com>
 <20210809064224.ctu3zxknn7s56gk3@linux.intel.com>
 <YRFKABg2MOJxcq+y@google.com>
 <20210810074037.mizpggevgyhed6rm@linux.intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <0ac41a07-beeb-161e-9e5d-e45477106c01@redhat.com>
Date:   Tue, 10 Aug 2021 11:25:27 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <20210810074037.mizpggevgyhed6rm@linux.intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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).

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.

Paolo