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 4387BC433F5 for ; Thu, 18 Nov 2021 07:46:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2348B61391 for ; Thu, 18 Nov 2021 07:46:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244001AbhKRHs7 (ORCPT ); Thu, 18 Nov 2021 02:48:59 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:52640 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244113AbhKRHsV (ORCPT ); Thu, 18 Nov 2021 02:48:21 -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-out2.suse.de (Postfix) with ESMTPS id 5760A1FD37; Thu, 18 Nov 2021 07:45:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637221520; 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=U+w/6qcGp66rTr9I94Sy80m7QueLxbiRPqzDu3h7BRw=; b=K6OQWFI/JMK+z+tVtN4GJPi8hmjDQIfLSP6H7QfNA1UBH7Ppggfpjli9nK2FYVCdrwc27h ot5CIuKTJmizvos3j6MSZgivPD9Cllk1Em3wGxbWZKX+KjaV4RDtc3lBlv/UHYxc7p71BP rHKOJnAWy4demiEjaR1hWnu6MDqZLQk= 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 E1C8F13CE6; Thu, 18 Nov 2021 07:45:19 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id pDzoNY8ElmFvRAAAMHmgww (envelope-from ); Thu, 18 Nov 2021 07:45:19 +0000 Subject: Re: [PATCH v3 1/4] x86/kvm: add boot parameter for adding vcpu-id bits To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Jonathan Corbet , Paolo Bonzini , 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> <7f10b8b4-e753-c977-f201-5ef17a6e81c8@suse.com> From: Juergen Gross Message-ID: <731540b4-e8fc-0322-5aa0-e134bc55a397@suse.com> Date: Thu, 18 Nov 2021 08:45:19 +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: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="BJWNkMgI9hOmEloIqiq80Rjg5tRoMpM2C" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --BJWNkMgI9hOmEloIqiq80Rjg5tRoMpM2C Content-Type: multipart/mixed; boundary="ooDNn4Igq5ipKsexUzCfKaCOO8sdrL8Fi"; protected-headers="v1" From: Juergen Gross To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Jonathan Corbet , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Message-ID: <731540b4-e8fc-0322-5aa0-e134bc55a397@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> <7f10b8b4-e753-c977-f201-5ef17a6e81c8@suse.com> In-Reply-To: --ooDNn4Igq5ipKsexUzCfKaCOO8sdrL8Fi Content-Type: multipart/mixed; boundary="------------395CF4152ECDAA3862AEB85D" Content-Language: en-US This is a multi-part message in MIME format. --------------395CF4152ECDAA3862AEB85D Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 18.11.21 00:46, Sean Christopherson wrote: > On Wed, Nov 17, 2021, Juergen Gross wrote: >> 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. >>> >>> In order to support higher vcpu-ids without generally increasing the >>> memory consumption of guests on the host (some guest structures conta= in >>> arrays sized by KVM_MAX_VCPU_IDS) add a boot parameter for adding som= e >>> 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 to= p >>> most level. >>> >>> 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. >>> >>> Calculating the maximum vcpu-id dynamically requires to allocate the >>> arrays using KVM_MAX_VCPU_IDS as the size dynamically. >>> >>> 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 memor= y >> depending on the max vcpu-id just as needed. >> >> Right now the only vcpu-id dependent memory is for the ioapic consisti= ng >> of a vcpu-id indexed bitmap and a vcpu-id indexed byte array (vectors)= =2E >> >> We could start with a minimal size when setting up an ioapic and exten= d >> the areas in case a new vcpu created would introduce a vcpu-id outside= >> the currently allocated memory. Both arrays are protected by the ioapi= c >> 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? >=20 > Why not have userspace state the max vcpu_id it intends to creates on a= per-VM > basis? Same end result, but doesn't require the complexity of realloca= ting the > I/O APIC stuff. >=20 And if the userspace doesn't do it (like today)? 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