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([2001:b07:add:ec09:c399:bc87:7b6c:fb2a]) by smtp.googlemail.com with ESMTPSA id g21sm2624155ejt.87.2021.11.25.23.57.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Nov 2021 23:57:04 -0800 (PST) Sender: Paolo Bonzini Message-ID: Date: Fri, 26 Nov 2021 08:56:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [RFC PATCH v3 54/59] KVM: X86: Introduce initial_tsc_khz in struct kvm_arch Content-Language: en-US To: Thomas Gleixner , isaku.yamahata@intel.com, Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , erdemaktas@google.com, Connor Kuehl , Sean Christopherson , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: isaku.yamahata@gmail.com, Xiaoyao Li References: <5ba3573c8b82fcbdc3f3994f6d4d2a3c40445be9.1637799475.git.isaku.yamahata@intel.com> <875ysghrp8.ffs@tglx> <741df444-5cd0-2049-f93a-c2521e4f426d@redhat.com> <87tufzhl56.ffs@tglx> From: Paolo Bonzini In-Reply-To: <87tufzhl56.ffs@tglx> 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 11/26/21 00:26, Thomas Gleixner wrote: > Paolo, > > On Thu, Nov 25 2021 at 23:13, Paolo Bonzini wrote: >> On 11/25/21 22:05, Thomas Gleixner wrote: >> If there are some patches that are actually independent, go ahead and >> submit them early. But more practically, for the bulk of the changes >> what you need to do is: >> >> 1) incorporate into patch 55 a version of tdx.c that essentially does >> KVM_BUG_ON or WARN_ON for each function. Temporarily keep the same huge >> patch that adds the remaining 2000 lines of tdx.c > > There is absolutely no reason to populate anything upfront at all. > Why? > > Simply because that whole muck cannot work until all pieces are in place. It can, sort of. It cannot run a complete guest, but it could in principle run a toy guest with a custom userspace, like the ones that make up tools/testing/selftests/kvm. (Note that KVM_BUG_ON marks the VM as bugged but doesn't hang the whole machine). AMD was working on infrastructure to do this for SEV and SEV-ES. > So why would you provide: > > handle_A(...) { BUG(); } > .. > handle_Z(...) { BUG(); } > > with all the invocations in the common emulation dispatcher: > > handle_stuff(reason) > { > switch(reason) { > case A: return handle_A(); > ... > case Z: return handle_Z(); > default: BUG(); > } > }; If it's a switch statement that's good, but the common case is more similar to this: vmx_handle_A(...) { ... } +tdx_handle_A(...) { ... } + +vt_handle_A(...) { + if (is_tdx(vcpu->kvm)) + tdx_handle_A(...); + else + vmx_handle_A(...); +} ... - .handle_A = vmx_handle_A, + .handle_A = vt_handle_A, And you could indeed do it in a single patch, without adding the stub tdx_handle_A upfront. But you would have code that is broken and who knows what the effects would be of calling vmx_handle_A on a TDX virtual machine. It could be an error, or it could be memory corruption. > In both scenarious you cannot boot a TDX guest until you reached $Z, but > in the gradual one you and the reviewers have the pleasure of looking at > one thing at a time. I think both of them are gradual. Not having the stubs might be a little more gradual, but it is a very minor issue for the reviewability of the whole thing. Paolo