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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.googlemail.com with ESMTPSA id x4-20020adfdd84000000b00207b60ed68esm1474940wrl.100.2022.04.13.01.38.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Apr 2022 01:38:28 -0700 (PDT) Message-ID: Date: Wed, 13 Apr 2022 10:38:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [RFC PATCH V3 2/4] KVM: X86: Introduce role.glevel for level expanded pagetable Content-Language: en-US To: Sean Christopherson , Lai Jiangshan Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Lai Jiangshan , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-doc@vger.kernel.org References: <20220330132152.4568-1-jiangshanlai@gmail.com> <20220330132152.4568-3-jiangshanlai@gmail.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/12/22 23:31, Sean Christopherson wrote: >> + unsigned glevel:4; > We don't need 4 bits for this. Crossing our fingers that we never had to shadow > a 2-level guest with a 6-level host, we can do: > > unsigned passthrough_delta:2; > > Where the field is ignored if direct=1, '0' for non-passthrough, and 1-3 to handle > shadow_root_level - guest_root_level. Basically the same idea as Paolo's smushing > of direct+passthrough into mapping_level, just dressed up differently. Basically, your passthrough_delta is level - glevel in Jiangshan's patches. You'll need 3 bits anyway when we remove direct later (that would be passthrough_delta == level). Regarding the naming: * If we keep Jiangshan's logic, I don't like the glevel name very much, any of mapping_level, target_level or direct_level would be clearer? * If we go with yours, I would call the field "passthrough_levels". Paolo