From mboxrd@z Thu Jan 1 00:00:00 1970 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=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 0647DC433FE for ; Fri, 3 Sep 2021 19:48:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE5ED60FE6 for ; Fri, 3 Sep 2021 19:48:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235994AbhICTtb (ORCPT ); Fri, 3 Sep 2021 15:49:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:52854 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231599AbhICTt3 (ORCPT ); Fri, 3 Sep 2021 15:49:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1630698508; 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: in-reply-to:in-reply-to:references:references; bh=DW68GxV6Lb0qE4ekh0Ivx+87OsRzETRMBE0QJs6OocI=; b=L060QxMNPEFMY3hqmNeLmRxpF1/0AJoikeGUi99ofOSc0voDXT1gLSajhuVNi1b1NUosPG +RQyXaJJCTgRNcf8DksijuPT2Sk24vkxk2qdTsvx0S9udYuyqkbajNpjm8wMqRqtf9Ji57 IFuTYU/3nDgIoMDPJRoaAvdBXFP0+fM= 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-417-2HDgqUOzOZWN2NPx5sx4EA-1; Fri, 03 Sep 2021 15:48:27 -0400 X-MC-Unique: 2HDgqUOzOZWN2NPx5sx4EA-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 4E2058042D6; Fri, 3 Sep 2021 19:48:25 +0000 (UTC) Received: from localhost (unknown [10.22.8.230]) by smtp.corp.redhat.com (Postfix) with ESMTP id A27675C1C5; Fri, 3 Sep 2021 19:48:24 +0000 (UTC) Date: Fri, 3 Sep 2021 15:48:24 -0400 From: Eduardo Habkost To: Juergen Gross Cc: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, Jonathan Corbet , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" Subject: Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits Message-ID: <20210903194824.lfjzeaab6ct72pxn@habkost.net> References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-3-jgross@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210903130808.30142-3-jgross@suse.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 03, 2021 at 03:08:03PM +0200, Juergen Gross wrote: > Today the maximum vcpu-id of a kvm guest's vcpu on x86 systems is set > via a #define in a header file. > > In order to support higher vcpu-ids without generally increasing the > memory consumption of guests on the host (some guest structures contain > arrays sized by KVM_MAX_VCPU_ID) add a boot parameter for adding some > bits to the vcpu-id. Additional bits are needed as the vcpu-id is > constructed via bit-wise concatenation of socket-id, core-id, etc. > As those ids maximum values are not always a power of 2, the vcpu-ids > are sparse. > > The additional number of bits needed is basically the number of > topology levels with a non-power-of-2 maximum value, excluding the top > most level. > > The default value of the new parameter will be to take the correct > setting from the host's topology. Having the default depend on the host topology makes the host behaviour unpredictable (which might be a problem when migrating VMs from another host with a different topology). Can't we just default to 2? > > Calculating the maximum vcpu-id dynamically requires to allocate the > arrays using KVM_MAX_VCPU_ID as the size dynamically. > > Signed-of-by: Juergen Gross > --- > V2: > - switch to specifying additional bits (based on comment by Vitaly > Kuznetsov) > > Signed-off-by: Juergen Gross > --- [...] > #define KVM_MAX_VCPUS 288 > #define KVM_SOFT_MAX_VCPUS 240 > -#define KVM_MAX_VCPU_ID 1023 > +#define KVM_MAX_VCPU_ID kvm_max_vcpu_id() [...] > +unsigned int kvm_max_vcpu_id(void) > +{ > + int n_bits = fls(KVM_MAX_VCPUS - 1); > + > + if (vcpu_id_add_bits < -1 || vcpu_id_add_bits > (32 - n_bits)) { > + pr_err("Invalid value of vcpu_id_add_bits=%d parameter!\n", > + vcpu_id_add_bits); > + vcpu_id_add_bits = -1; > + } > + > + if (vcpu_id_add_bits >= 0) { > + n_bits += vcpu_id_add_bits; > + } else { > + n_bits++; /* One additional bit for core level. */ > + if (topology_max_die_per_package() > 1) > + n_bits++; /* One additional bit for die level. */ > + } > + > + if (!n_bits) > + n_bits = 1; > + > + return (1U << n_bits) - 1; The largest possible VCPU ID is not KVM_MAX_VCPU_ID, it's (KVM_MAX_VCPU_ID - 1). This is enforced by kvm_vm_ioctl_create_vcpu(). That would mean KVM_MAX_VCPU_ID should be (1 << n_bits) instead of ((1 << n_bits) - 1), wouldn't it? > +} > +EXPORT_SYMBOL_GPL(kvm_max_vcpu_id); > + > /* > * Restoring the host value for MSRs that are only consumed when running in > * usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU > -- > 2.26.2 > -- Eduardo