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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D46EAC433F5 for ; Wed, 17 Nov 2021 06:59:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B901E6101C for ; Wed, 17 Nov 2021 06:59:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234053AbhKQHCb (ORCPT ); Wed, 17 Nov 2021 02:02:31 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:47062 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230086AbhKQHC3 (ORCPT ); Wed, 17 Nov 2021 02:02:29 -0500 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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-out1.suse.de (Postfix) with ESMTPS id 9F71F218F6; Wed, 17 Nov 2021 06:59:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637132370; 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=jFLry+57aO+/X2xFtkejmH6hxoRwRJTwEqp3PTJ65fU=; b=fyZg/KscL4weKQwyRVsZb+k1WNjKVX+SU2srVMA0oEEOhBnvNU8LHsuoyEURitGQLDswUT s5gP0A+aqbrjdeE96cWibIMLt196wVtmwTDI1T0HSun3P7ZzBkMSpuncyO3txBoABcyqwt KomX+t/oi6Tm9lcEs2HtIMZHAUcthTg= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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 imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 3320B13BC3; Wed, 17 Nov 2021 06:59:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id GU53ClKolGG8QgAAMHmgww (envelope-from ); Wed, 17 Nov 2021 06:59:30 +0000 To: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Jonathan Corbet , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" References: <20211116141054.17800-1-jgross@suse.com> <20211116141054.17800-2-jgross@suse.com> From: Juergen Gross Subject: Re: [PATCH v3 1/4] x86/kvm: add boot parameter for adding vcpu-id bits Message-ID: <7f10b8b4-e753-c977-f201-5ef17a6e81c8@suse.com> Date: Wed, 17 Nov 2021 07:59:29 +0100 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: <20211116141054.17800-2-jgross@suse.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="5eo5bD3r9P3bOCT2gHXysSF26z3K2TFTi" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --5eo5bD3r9P3bOCT2gHXysSF26z3K2TFTi Content-Type: multipart/mixed; boundary="np1SL7B1cJZKUl5TWNeDfs8AlCPuzlnt7"; protected-headers="v1" From: Juergen Gross To: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Jonathan Corbet , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Message-ID: <7f10b8b4-e753-c977-f201-5ef17a6e81c8@suse.com> Subject: Re: [PATCH v3 1/4] x86/kvm: add boot parameter for adding vcpu-id bits References: <20211116141054.17800-1-jgross@suse.com> <20211116141054.17800-2-jgross@suse.com> In-Reply-To: <20211116141054.17800-2-jgross@suse.com> --np1SL7B1cJZKUl5TWNeDfs8AlCPuzlnt7 Content-Type: multipart/mixed; boundary="------------9267E211171704C5A3D52120" Content-Language: en-US This is a multi-part message in MIME format. --------------9267E211171704C5A3D52120 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 16.11.21 15:10, 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. >=20 > 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_IDS) 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. >=20 > 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. >=20 > The default value of the new parameter will be 2 in order to support > today's possible topologies. The special value of -1 will use the > number of bits needed for a guest with the current host's topology. >=20 > Calculating the maximum vcpu-id dynamically requires to allocate the > arrays using KVM_MAX_VCPU_IDS as the size dynamically. >=20 > Signed-of-by: Juergen Gross Just thought about vcpu-ids a little bit more. It would be possible to replace the topology games completely by an arbitrary rather high vcpu-id limit (65536?) and to allocate the memory depending on the max vcpu-id just as needed. Right now the only vcpu-id dependent memory is for the ioapic consisting of a vcpu-id indexed bitmap and a vcpu-id indexed byte array (vectors). We could start with a minimal size when setting up an ioapic and extend the areas in case a new vcpu created would introduce a vcpu-id outside the currently allocated memory. Both arrays are protected by the ioapic specific lock (at least I couldn't spot any unprotected usage when looking briefly into the code), so reallocating those arrays shouldn't be hard. In case of ENOMEM the related vcpu creation would just fail. Thoughts? 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