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=-16.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A30E1C433EF for ; Mon, 6 Sep 2021 04:46:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A0F06103C for ; Mon, 6 Sep 2021 04:46:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238664AbhIFErf (ORCPT ); Mon, 6 Sep 2021 00:47:35 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:36086 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236292AbhIFErc (ORCPT ); Mon, 6 Sep 2021 00:47:32 -0400 Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 608F21FEC0; Mon, 6 Sep 2021 04:46:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1630903586; h=from:from:reply-to: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=5WXZWDjsL6VCDzFfKsy+fr5w2Ib5Q48se+K6nAixw7A=; b=skiUEYbZPkGoKoSnNKDcWM2FTl6pRFomATdSKpYlwHm+RVUcnGhls0q3bU138VCdwYyHAn Rkh/CE3wMrsCbW8E6Q274XJ+Imtmo22cZt7aKVwITgcELWNkbAgZlhhDVBdi7D79TrR29m WcqcE3xs8V6NIepJ9N/RHBbbPcpCw8M= Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id CB30A1332A; Mon, 6 Sep 2021 04:46:25 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id qWCDLyGdNWFDQwAAGKfGzw (envelope-from ); Mon, 06 Sep 2021 04:46:25 +0000 To: Eduardo Habkost 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" References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-3-jgross@suse.com> <20210903194824.lfjzeaab6ct72pxn@habkost.net> From: Juergen Gross Subject: Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits Message-ID: <2f7d511e-e846-e6a4-f180-987511518f42@suse.com> Date: Mon, 6 Sep 2021 06:46:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210903194824.lfjzeaab6ct72pxn@habkost.net> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="qJYM4kX82J82dgMD9nuy8n4hbZ6zojjbg" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --qJYM4kX82J82dgMD9nuy8n4hbZ6zojjbg Content-Type: multipart/mixed; boundary="qU4uyZzhiMzt6qlPfC6tu7Ah3DhhJy0mE"; protected-headers="v1" From: Juergen Gross To: Eduardo Habkost 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" Message-ID: <2f7d511e-e846-e6a4-f180-987511518f42@suse.com> Subject: Re: [PATCH v2 2/6] x86/kvm: add boot parameter for adding vcpu-id bits References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-3-jgross@suse.com> <20210903194824.lfjzeaab6ct72pxn@habkost.net> In-Reply-To: <20210903194824.lfjzeaab6ct72pxn@habkost.net> --qU4uyZzhiMzt6qlPfC6tu7Ah3DhhJy0mE Content-Type: multipart/mixed; boundary="------------0F5B31BAE14E271D71F849BD" Content-Language: en-US This is a multi-part message in MIME format. --------------0F5B31BAE14E271D71F849BD Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 03.09.21 21:48, Eduardo Habkost wrote: > 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 contai= n >> 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. >=20 > 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? Okay, fine with me. >=20 >> >> 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 =3D 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=3D%d parameter!\n", >> + vcpu_id_add_bits); >> + vcpu_id_add_bits =3D -1; >> + } >> + >> + if (vcpu_id_add_bits >=3D 0) { >> + n_bits +=3D 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 =3D 1; >> + >> + return (1U << n_bits) - 1; >=20 > 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(). >=20 > That would mean KVM_MAX_VCPU_ID should be (1 << n_bits) instead > of ((1 << n_bits) - 1), wouldn't it? Oh, indeed. I have been fooled by the IMO bad naming of this macro. The current value 1023 suggests it is not only me having been fooled. Shouldn't it be named "KVM_MAX_VCPU_IDS" instead? 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