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 52100C4332F for ; Thu, 18 Nov 2021 07:44:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3755460F36 for ; Thu, 18 Nov 2021 07:44:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244081AbhKRHrI (ORCPT ); Thu, 18 Nov 2021 02:47:08 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:52574 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244023AbhKRHqd (ORCPT ); Thu, 18 Nov 2021 02:46:33 -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 082CF1FD35; Thu, 18 Nov 2021 07:43:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637221413; 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=cYDfG1oWSZbpBbHPdOX+BBO1kGppbDRZd6YB8IrMIt4=; b=GoW67FhrZiEQtZbWrTUGjiuO1TLmmGJatHDV07tfXVYycEOebd3Trh9TuO7lIkVidGyiLV pmsuLca+A3mZIVabrNdkMeU7X0JZZ7aRYsZ0GvceZv/N1LteG5sbz6ychGzF+SOzGtVBcz cl81O0BddObSuJ02niDMkgEHuNAbWD4= 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 8026813CE6; Thu, 18 Nov 2021 07:43:32 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id ncWsHSQElmG0QwAAMHmgww (envelope-from ); Thu, 18 Nov 2021 07:43:32 +0000 To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, 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> <20211116141054.17800-4-jgross@suse.com> From: Juergen Gross Subject: Re: [PATCH v3 3/4] x86/kvm: add max number of vcpus for hyperv emulation Message-ID: Date: Thu, 18 Nov 2021 08:43:31 +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="5cBUQoToneO8V1pOyzcWLmtIJYL04gXMC" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --5cBUQoToneO8V1pOyzcWLmtIJYL04gXMC Content-Type: multipart/mixed; boundary="LPl7Rl1ITYfjr8Kctme8DZCrMQ2s3J761"; protected-headers="v1" From: Juergen Gross To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Message-ID: Subject: Re: [PATCH v3 3/4] x86/kvm: add max number of vcpus for hyperv emulation References: <20211116141054.17800-1-jgross@suse.com> <20211116141054.17800-4-jgross@suse.com> In-Reply-To: --LPl7Rl1ITYfjr8Kctme8DZCrMQ2s3J761 Content-Type: multipart/mixed; boundary="------------02CD9F29A3AC9F1BB7F0C3BA" Content-Language: en-US This is a multi-part message in MIME format. --------------02CD9F29A3AC9F1BB7F0C3BA Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 17.11.21 21:50, Sean Christopherson wrote: > On Tue, Nov 16, 2021, Juergen Gross wrote: >> When emulating Hyperv the theoretical maximum of vcpus supported is >> 4096, as this is the architectural limit for sending IPIs via the PV >> interface. >> >> For restricting the actual supported number of vcpus for that case >> introduce another define KVM_MAX_HYPERV_VCPUS and set it to 1024, like= >> today's KVM_MAX_VCPUS. Make both values unsigned ones as this will be >> needed later. >> >> The actual number of supported vcpus for Hyperv emulation will be the >> lower value of both defines. >> >> This is a preparation for a future boot parameter support of the max >> number of vcpus for a KVM guest. >> >> Signed-off-by: Juergen Gross >> --- >> V3: >> - new patch >> --- >> arch/x86/include/asm/kvm_host.h | 3 ++- >> arch/x86/kvm/hyperv.c | 15 ++++++++------- >> 2 files changed, 10 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kv= m_host.h >> index 886930ec8264..8ea03ff01c45 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -38,7 +38,8 @@ >> =20 >> #define __KVM_HAVE_ARCH_VCPU_DEBUGFS >> =20 >> -#define KVM_MAX_VCPUS 1024 >> +#define KVM_MAX_VCPUS 1024U >> +#define KVM_MAX_HYPERV_VCPUS 1024U >=20 > I don't see any reason to put this in kvm_host.h, it should never be us= ed outside > of hyperv.c. Okay, fine with me. >=20 >> #define KVM_MAX_VCPU_IDS kvm_max_vcpu_ids() >> /* memory slots that are not exposed to userspace */ >> #define KVM_PRIVATE_MEM_SLOTS 3 >> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c >> index 4a555f32885a..c0fa837121f1 100644 >> --- a/arch/x86/kvm/hyperv.c >> +++ b/arch/x86/kvm/hyperv.c >> @@ -41,7 +41,7 @@ >> /* "Hv#1" signature */ >> #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648 >> =20 >> -#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 6= 4) >> +#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_HYPERV_V= CPUS, 64) >> =20 >> static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer, >> bool vcpu_kick); >> @@ -166,7 +166,7 @@ static struct kvm_vcpu *get_vcpu_by_vpidx(struct k= vm *kvm, u32 vpidx) >> struct kvm_vcpu *vcpu =3D NULL; >> int i; >> =20 >> - if (vpidx >=3D KVM_MAX_VCPUS) >> + if (vpidx >=3D min(KVM_MAX_VCPUS, KVM_MAX_HYPERV_VCPUS)) >=20 > IMO, this is conceptually wrong. KVM should refuse to allow Hyper-V to= be enabled > if the max number of vCPUs exceeds what can be supported, or should ref= use to create TBH, I wasn't sure where to put this test. Is there a guaranteed sequence of ioctl()s regarding vcpu creation (or setting the max number of vcpus) and the Hyper-V enabling? > the vCPUs. I agree it makes sense to add a Hyper-V specific limit, sin= ce there are > Hyper-V structures that have a hard limit, but detection of violations = should be a > BUILD_BUG_ON, not a silent failure at runtime. >=20 A BUILD_BUG_ON won't be possible with KVM_MAX_VCPUS being selecteble via boot parameter. 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