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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id p24sm13811998edt.5.2021.04.06.04.42.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Apr 2021 04:42:35 -0700 (PDT) From: Vitaly Kuznetsov To: Paolo Bonzini , qemu-devel@nongnu.org Subject: Re: [PATCH 0/2] i386: Fix interrupt based Async PF enablement In-Reply-To: References: <20210401151957.408028-1-vkuznets@redhat.com> Date: Tue, 06 Apr 2021 13:42:35 +0200 Message-ID: <87sg43d4gk.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vkuznets@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Michael S. Tsirkin" , Richard Henderson , Eduardo Habkost , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Paolo Bonzini writes: > On 01/04/21 17:19, Vitaly Kuznetsov wrote: >> I noticed two issues with 'kvm-asyncpf-int' enablement: >> 1) We forgot to add to to kvm_default_props[] so it doesn't get enabled >> automatically (unless '-cpu host' is used or the feature is enabled >> manually on the command line) >> 2) We forgot to disable it for older machine types to preserve migration. >> This went unnoticed because of 1) I believe. >> >> Vitaly Kuznetsov (2): >> i386: Add 'kvm-asyncpf-int' to kvm_default_props array >> i386: Disable 'kvm-asyncpf-int' feature for machine types <= 5.1 >> >> hw/i386/pc.c | 1 + >> target/i386/cpu.c | 1 + >> 2 files changed, 2 insertions(+) >> > > Wasn't this intentional to avoid requiring a new kernel version? I think I forgot the initial plan :-( The problem is that after we disabled the original APF (#PF based) almost nobody is using the feature as it needs to be enabled explicitly on the command line. Several considerations regarding the default: if your kernel doesn't support the feature you get as much as a warning: qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.40000001H:EAX.kvm-asyncpf-int [bit 14] older machine types are still available (I disable it for <= 5.1 but we can consider disabling it for 5.2 too). The feature is upstream since Linux 5.8, I know that QEMU supports much older kernels but this doesn't probably mean that we can't enable new KVM PV features unless all supported kernels have it, we'd have to wait many years otherwise. -- Vitaly