From patchwork Thu Jul 22 12:15:26 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vitaly Kuznetsov X-Patchwork-Id: 12393979 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27E18C6377D for ; Thu, 22 Jul 2021 12:20:10 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C1AF06135A for ; Thu, 22 Jul 2021 12:20:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C1AF06135A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42738 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m6XgO-0001kK-UQ for qemu-devel@archiver.kernel.org; Thu, 22 Jul 2021 08:20:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45734) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m6Xc1-0003IC-J0 for qemu-devel@nongnu.org; Thu, 22 Jul 2021 08:15:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:20964) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m6Xc0-0001h1-09 for qemu-devel@nongnu.org; Thu, 22 Jul 2021 08:15:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626956135; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Z1tIU2YHphnYuT9wydQ/esWuZWRJ4ptwamQw8mUHyLs=; b=Q7R31zK1OorWA9aqNCg7QP4IDxtHWiopNvnzsm/VguNZqys8gcel1PBAorRRDuh7GL1sbo HM5nx6hWxaV2tk2sLOArBzvZFusAOh8BJlmbNypE3GRg137aHE1Mqgachy6yu6p+IWEW7s TI4pAEUNu9B/2mcseCxbmL4ACeYNfF0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-322-vAW126CXNCGR8Fb1RHtu5A-1; Thu, 22 Jul 2021 08:15:34 -0400 X-MC-Unique: vAW126CXNCGR8Fb1RHtu5A-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 85F8F92500 for ; Thu, 22 Jul 2021 12:15:33 +0000 (UTC) Received: from vitty.brq.redhat.com (unknown [10.40.195.41]) by smtp.corp.redhat.com (Postfix) with ESMTP id D93595FC03; Thu, 22 Jul 2021 12:15:31 +0000 (UTC) From: Vitaly Kuznetsov To: qemu-devel@nongnu.org, Eduardo Habkost Subject: [PATCH 1/3] docs: Briefly describe KVM PV features Date: Thu, 22 Jul 2021 14:15:26 +0200 Message-Id: <20210722121528.258426-2-vkuznets@redhat.com> In-Reply-To: <20210722121528.258426-1-vkuznets@redhat.com> References: <20210722121528.258426-1-vkuznets@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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 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: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.472, 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: Paolo Bonzini , Marcelo Tosatti , Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" KVM PV features don't seem to be documented anywhere, in particular, the fact that some of the features are enabled by default and some are not can only be figured out from the code. Signed-off-by: Vitaly Kuznetsov --- docs/kvm-pv.txt | 92 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 92 insertions(+) create mode 100644 docs/kvm-pv.txt diff --git a/docs/kvm-pv.txt b/docs/kvm-pv.txt new file mode 100644 index 000000000000..84ad7fa60f8d --- /dev/null +++ b/docs/kvm-pv.txt @@ -0,0 +1,92 @@ +KVM paravirtualized features +============================ + + +1. Description +=============== +In some cases when implementing a hardware interface in software is slow, KVM +implements its own paravirtualized interfaces. + +2. Setup +========= +KVM PV features are represented as CPU flags. The following features are enabled +by default for any CPU model when KVM is enabled: + kvmclock + kvm-nopiodelay + kvm-asyncpf + kvm-steal-time + kvm-pv-eoi + kvmclock-stable-bit + +'kvm-msi-ext-dest-id' feature is enabled by default in x2apic mode with split +irqchip (e.g. "-machine ...,kernel-irqchip=split -cpu ...,x2apic"). + +Note: when cpu model 'host' is used, QEMU passes through all KVM PV features +exposed by KVM to the guest. + +3. Existing features +==================== + +3.1. kvmclock +================ +This feature exposes KVM specific PV clocksource to the guest. + +3.2. kvm-nopiodelay +=================== +The guest doesn't need to perform delays on PIO operations. + +3.3. kvm-mmu +============ +This feature is deprecated. + +3.4. kvm-asyncpf +================ +Enables asynchronous page fault mechanism. Note: since Linux-5.10 the feature is +deprecated and not enabled by KVM. Use "kvm-asyncpf-int" instead. + +3.5. kvm-steal-time +=================== +Enables stolen (when guest vCPU is not running) time accounting. + +3.6. kvm-pv-eoi +=============== +Enables paravirtualized end-of-interrupt signaling. + +3.7. kvm-pv-unhalt +================== +Enables paravirtualized spinlocks support. + +3.8. kvm-pv-tlb-flush +===================== +Enables paravirtualized TLB flush mechanism. + +3.9. kvm-pv-ipi +=============== +Enables paravirtualized IPI mechanism. + +3.10. kvm-poll-control +====================== +Enables host-side polling on HLT control from the guest. + +3.11. kvm-pv-sched-yield +======================== +Enables paravirtualized sched yield feature. + +3.12. kvm-asyncpf-int +===================== +Enables interrupt based asynchronous page fault mechanism. + +3.13. kvm-msi-ext-dest-id +========================= +Support 'Extended Destination ID' for external interrupts. The feature allows +to use up to 32768 CPUs without IRQ remapping (but other limits may apply making +the number of supported vCPUs for a given configuration lower). + +3.14. kvmclock-stable-bit +========================= +Tells the guest that guest visible TSC value can be fully trusted for kvmclock +computations and no warps are expected. + +4. Useful links +================ +Please refer to Documentation/virt/kvm in Linux for additional detail.