From patchwork Tue Nov 16 14:10:54 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 12622441 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 45AE7C433FE for ; Tue, 16 Nov 2021 14:11:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2AB2A61BFB for ; Tue, 16 Nov 2021 14:11:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237125AbhKPOOQ (ORCPT ); Tue, 16 Nov 2021 09:14:16 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:40764 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237169AbhKPON6 (ORCPT ); Tue, 16 Nov 2021 09:13:58 -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 6A06A1FD37; Tue, 16 Nov 2021 14:11:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637071860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eUzARzMdGIdgZhKMMm7MjS/I2ys+aHQmiheFYNSahmg=; b=YMdoxtQ/UmnVX7LVsdDt0A4V1t8OsHiy0lGMBX0bfIpqPZFGWSDz0+j5ISu6Wu+rcSND7z ckSQQw2/BcITl6FfGtwclZEhvDBho0PdTVnhoAu7/m5Cq4S8AocdNNWhtfGq2mzjGOgZVQ QyrGiPQIkFZgEszDFk3r005h9iDfAYU= 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 017ED13F75; Tue, 16 Nov 2021 14:10:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id qFWaOvO7k2ExEQAAMHmgww (envelope-from ); Tue, 16 Nov 2021 14:10:59 +0000 From: Juergen Gross To: kvm@vger.kernel.org, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Juergen Gross , 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" Subject: [PATCH v3 4/4] x86/kvm: add boot parameter for setting max number of vcpus per guest Date: Tue, 16 Nov 2021 15:10:54 +0100 Message-Id: <20211116141054.17800-5-jgross@suse.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20211116141054.17800-1-jgross@suse.com> References: <20211116141054.17800-1-jgross@suse.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Today the maximum number of vcpus of a kvm guest is set via a #define in a header file. In order to support higher vcpu numbers for guests without generally increasing the memory consumption of guests on the host especially on very large systems add a boot parameter for specifying the number of allowed vcpus for guests. The default will still be the current setting of 1024. The value 0 has the special meaning to limit the number of possible vcpus to the number of possible cpus of the host. Signed-off-by: Juergen Gross Signed-off-by: Sean Christopherson --- V3: - rebase --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ arch/x86/include/asm/kvm_host.h | 5 ++++- arch/x86/kvm/x86.c | 9 ++++++++- 3 files changed, 19 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index e269c3f66ba4..409a72c2d91b 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2445,6 +2445,13 @@ feature (tagged TLBs) on capable Intel chips. Default is 1 (enabled) + kvm.max_vcpus= [KVM,X86] Set the maximum allowed numbers of vcpus per + guest. The special value 0 sets the limit to the number + of physical cpus possible on the host (including not + yet hotplugged cpus). Higher values will result in + slightly higher memory consumption per guest. + Default: 1024 + kvm.vcpu_id_add_bits= [KVM,X86] The vcpu-ids of guests are sparse, as they are constructed by bit-wise concatenation of the ids of diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 8ea03ff01c45..8566e278ca91 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -38,7 +38,8 @@ #define __KVM_HAVE_ARCH_VCPU_DEBUGFS -#define KVM_MAX_VCPUS 1024U +#define KVM_DEFAULT_MAX_VCPUS 1024U +#define KVM_MAX_VCPUS max_vcpus #define KVM_MAX_HYPERV_VCPUS 1024U #define KVM_MAX_VCPU_IDS kvm_max_vcpu_ids() /* memory slots that are not exposed to userspace */ @@ -1611,6 +1612,8 @@ extern u64 kvm_max_tsc_scaling_ratio; extern u64 kvm_default_tsc_scaling_ratio; /* bus lock detection supported? */ extern bool kvm_has_bus_lock_exit; +/* maximum number of vcpus per guest */ +extern unsigned int max_vcpus; /* maximum vcpu-id */ unsigned int kvm_max_vcpu_ids(void); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a388acdc5eb0..3571ea34135b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -190,9 +190,13 @@ module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR); static int __read_mostly vcpu_id_add_bits = 2; module_param(vcpu_id_add_bits, int, S_IRUGO); +unsigned int __read_mostly max_vcpus = KVM_DEFAULT_MAX_VCPUS; +module_param(max_vcpus, uint, S_IRUGO); +EXPORT_SYMBOL_GPL(max_vcpus); + unsigned int kvm_max_vcpu_ids(void) { - int n_bits = fls(KVM_MAX_VCPUS - 1); + int n_bits = fls(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", @@ -11251,6 +11255,9 @@ int kvm_arch_hardware_setup(void *opaque) if (boot_cpu_has(X86_FEATURE_XSAVES)) rdmsrl(MSR_IA32_XSS, host_xss); + if (max_vcpus == 0) + max_vcpus = num_possible_cpus(); + kvm_pcpu_vcpu_mask = __alloc_percpu(KVM_VCPU_MASK_SZ, sizeof(unsigned long)); if (!kvm_pcpu_vcpu_mask) {