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([2001:b07:6468:f312:60bb:f5bd:83ff:ec47]) by smtp.gmail.com with ESMTPSA id w12sm4196501wmk.12.2020.05.15.08.59.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 May 2020 08:59:44 -0700 (PDT) Subject: Re: [PATCH 2/8] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info To: Vivek Goyal , Sean Christopherson Cc: Vitaly Kuznetsov , kvm@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , Wanpeng Li , Jim Mattson , Gavin Shan , Peter Zijlstra , linux-kernel@vger.kernel.org References: <20200511164752.2158645-1-vkuznets@redhat.com> <20200511164752.2158645-3-vkuznets@redhat.com> <20200512152709.GB138129@redhat.com> <87o8qtmaat.fsf@vitty.brq.redhat.com> <20200512155339.GD138129@redhat.com> <20200512175017.GC12100@linux.intel.com> <20200513125241.GA173965@redhat.com> From: Paolo Bonzini Message-ID: <0733213c-9514-4b04-6356-cf1087edd9cf@redhat.com> Date: Fri, 15 May 2020 17:59:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200513125241.GA173965@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/05/20 14:52, Vivek Goyal wrote: >>> Also, type of event should not necessarily be tied to delivery method. >>> For example if we end up introducing say, "KVM_PV_REASON_PAGE_ERROR", then >>> I would think that event can be injected both using exception (#PF or #VE) >>> as well as interrupt (depending on state of system). >> Why bother preserving backwards compatibility? > New machanism does not have to support old guests but old mechanism > should probably continue to work and deprecated slowly, IMHO. Otherwise > guests which were receiving async page faults will suddenly stop getting > it over hypervisor upgrade and possibly see drop in performance. Unfortunately, the old mechanism was broken enough, and in enough different ways, that it's better to just drop it. The new one using #VE is not coming very soon (we need to emulate it for