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 EB8A7C433EF for ; Thu, 11 Nov 2021 19:36:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C91376134F for ; Thu, 11 Nov 2021 19:36:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233299AbhKKTj1 (ORCPT ); Thu, 11 Nov 2021 14:39:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:45450 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229710AbhKKTj0 (ORCPT ); Thu, 11 Nov 2021 14:39:26 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3AD2961252; Thu, 11 Nov 2021 19:36:37 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mlFsA-004t5h-VL; Thu, 11 Nov 2021 19:36:35 +0000 MIME-Version: 1.0 Date: Thu, 11 Nov 2021 19:36:34 +0000 From: Marc Zyngier To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Eduardo Habkost , Andrew Jones , Huacai Chen , Aleksandar Markovic , Anup Patel , Paul Mackerras , Michael Ellerman , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS In-Reply-To: <20211111162746.100598-2-vkuznets@redhat.com> References: <20211111162746.100598-1-vkuznets@redhat.com> <20211111162746.100598-2-vkuznets@redhat.com> User-Agent: Roundcube Webmail/1.4.11 Message-ID: X-Sender: maz@kernel.org Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: vkuznets@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com, wanpengli@tencent.com, jmattson@google.com, ehabkost@redhat.com, drjones@redhat.com, chenhuacai@kernel.org, aleksandar.qemu.devel@gmail.com, anup.patel@wdc.com, paulus@ozlabs.org, mpe@ellerman.id.au, kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vitaly, On 2021-11-11 16:27, Vitaly Kuznetsov wrote: > It doesn't make sense to return the recommended maximum number of > vCPUs which exceeds the maximum possible number of vCPUs. > > Signed-off-by: Vitaly Kuznetsov > --- > arch/arm64/kvm/arm.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 7838e9fb693e..391dc7a921d5 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -223,7 +223,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, > long ext) > r = 1; > break; > case KVM_CAP_NR_VCPUS: > - r = num_online_cpus(); > + if (kvm) > + r = min_t(unsigned int, num_online_cpus(), > + kvm->arch.max_vcpus); > + else > + r = min_t(unsigned int, num_online_cpus(), > + kvm_arm_default_max_vcpus()); > break; > case KVM_CAP_MAX_VCPUS: > case KVM_CAP_MAX_VCPU_ID: This looks odd. This means that depending on the phase userspace is in while initialising the VM, KVM_CAP_NR_VCPUS can return one thing or the other. For example, I create a VM on a 32 CPU system, NR_VCPUS says 32. I create a GICv2 interrupt controller, it now says 8. That's a change in behaviour that is visible by userspace, which I'm keen on avoiding. I'd rather have the kvm and !kvm cases return the same thing. Thanks, M. -- Jazz is not dead. It just smells funny... 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 9D187C433F5 for ; Thu, 11 Nov 2021 19:38:28 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 64DD6611C9 for ; Thu, 11 Nov 2021 19:38:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 64DD6611C9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:Subject:Cc:To:From :Date:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; 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Thu, 11 Nov 2021 19:36:37 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mlFsA-004t5h-VL; Thu, 11 Nov 2021 19:36:35 +0000 MIME-Version: 1.0 Date: Thu, 11 Nov 2021 19:36:34 +0000 From: Marc Zyngier To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Eduardo Habkost , Andrew Jones , Huacai Chen , Aleksandar Markovic , Anup Patel , Paul Mackerras , Michael Ellerman , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS In-Reply-To: <20211111162746.100598-2-vkuznets@redhat.com> References: <20211111162746.100598-1-vkuznets@redhat.com> <20211111162746.100598-2-vkuznets@redhat.com> User-Agent: Roundcube Webmail/1.4.11 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: vkuznets@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com, wanpengli@tencent.com, jmattson@google.com, ehabkost@redhat.com, drjones@redhat.com, chenhuacai@kernel.org, aleksandar.qemu.devel@gmail.com, anup.patel@wdc.com, paulus@ozlabs.org, mpe@ellerman.id.au, kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211111_113638_787404_5119ADFA X-CRM114-Status: GOOD ( 19.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Vitaly, On 2021-11-11 16:27, Vitaly Kuznetsov wrote: > It doesn't make sense to return the recommended maximum number of > vCPUs which exceeds the maximum possible number of vCPUs. > > Signed-off-by: Vitaly Kuznetsov > --- > arch/arm64/kvm/arm.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 7838e9fb693e..391dc7a921d5 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -223,7 +223,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, > long ext) > r = 1; > break; > case KVM_CAP_NR_VCPUS: > - r = num_online_cpus(); > + if (kvm) > + r = min_t(unsigned int, num_online_cpus(), > + kvm->arch.max_vcpus); > + else > + r = min_t(unsigned int, num_online_cpus(), > + kvm_arm_default_max_vcpus()); > break; > case KVM_CAP_MAX_VCPUS: > case KVM_CAP_MAX_VCPU_ID: This looks odd. This means that depending on the phase userspace is in while initialising the VM, KVM_CAP_NR_VCPUS can return one thing or the other. For example, I create a VM on a 32 CPU system, NR_VCPUS says 32. I create a GICv2 interrupt controller, it now says 8. That's a change in behaviour that is visible by userspace, which I'm keen on avoiding. I'd rather have the kvm and !kvm cases return the same thing. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel