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([2001:b07:6468:f312:d107:d3ba:83ae:307e]) by smtp.gmail.com with ESMTPSA id l10sm14977264wru.59.2020.09.20.09.42.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 20 Sep 2020 09:42:39 -0700 (PDT) Subject: Re: [PATCH v4 2/2] KVM: nSVM: implement ondemand allocation of the nested state To: Sean Christopherson Cc: Maxim Levitsky , kvm@vger.kernel.org, Vitaly Kuznetsov , Ingo Molnar , Wanpeng Li , "H. Peter Anvin" , Borislav Petkov , Jim Mattson , Joerg Roedel , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , linux-kernel@vger.kernel.org, Thomas Gleixner References: <20200917101048.739691-1-mlevitsk@redhat.com> <20200917101048.739691-3-mlevitsk@redhat.com> <20200917162942.GE13522@sjchrist-ice> <20200920161602.GA17325@linux.intel.com> From: Paolo Bonzini Message-ID: Date: Sun, 20 Sep 2020 18:42:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200920161602.GA17325@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/09/20 18:16, Sean Christopherson wrote: >> Maxim, your previous version was adding some error handling to >> kvm_x86_ops.set_efer. I don't remember what was the issue; did you have >> any problems propagating all the errors up to KVM_SET_SREGS (easy), >> kvm_set_msr (harder) etc.? > I objected to letting .set_efer() return a fault. So did I, and that's why we get KVM_REQ_OUT_OF_MEMORY. But it was more of an "it's ugly and it ought not to fail" thing than something I could pinpoint. It looks like we agree, but still we have to choose the lesser evil? Paolo > A relatively minor issue is > the code in vmx_set_efer() that handles lack of EFER because technically KVM > can emulate EFER.SCE+SYSCALL without supporting EFER in hardware. Returning > success/'0' would avoid that particular issue. My primary concern is that I'd > prefer not to add another case where KVM can potentially ignore a fault > indicated by a helper, a la vmx_set_cr4().