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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C83CC433EF for ; Thu, 13 Jan 2022 14:29:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235668AbiAMO3I (ORCPT ); Thu, 13 Jan 2022 09:29:08 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60213 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231161AbiAMO3H (ORCPT ); Thu, 13 Jan 2022 09:29:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642084146; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KD9x1FnPOWiMxqn8PJ52imgGWmsMrgv0XjSE1mjBD5E=; b=hHPi/4dD52evyAxlt/0dQTLVkN4zCbCW5Vl/ZiYSnPaIpwgMojfq47xlpcn5I4i5xWzZ6f ErOwpC0l9vmriNSKGAFe3be8KpWo3qXpy/zkkMy66PDbo2S4yc2VghCz3GMwrGkhKDKfQE BNEZMFl9lV3XcIITCEg32m0wq88gbvI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-104-teqkYBZ0P3mt-ceJzowZSw-1; Thu, 13 Jan 2022 09:29:03 -0500 X-MC-Unique: teqkYBZ0P3mt-ceJzowZSw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2A4EB8024C7; Thu, 13 Jan 2022 14:29:02 +0000 (UTC) Received: from starship (unknown [10.40.192.177]) by smtp.corp.redhat.com (Postfix) with ESMTP id 028AD108C0; Thu, 13 Jan 2022 14:28:51 +0000 (UTC) Message-ID: <7e7c7e22f8b1b1695d26d9e19a767b87c679df93.camel@redhat.com> Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN From: Maxim Levitsky To: Vitaly Kuznetsov , Paolo Bonzini , Igor Mammedov Cc: kvm@vger.kernel.org, Sean Christopherson , Wanpeng Li , Jim Mattson , linux-kernel@vger.kernel.org Date: Thu, 13 Jan 2022 16:28:49 +0200 In-Reply-To: <87bl0gnfy5.fsf@redhat.com> References: <20211122175818.608220-1-vkuznets@redhat.com> <20211122175818.608220-3-vkuznets@redhat.com> <16368a89-99ea-e52c-47b6-bd006933ec1f@redhat.com> <20211227183253.45a03ca2@redhat.com> <61325b2b-dc93-5db2-2d0a-dd0900d947f2@redhat.com> <87mtkdqm7m.fsf@redhat.com> <20220103104057.4dcf7948@redhat.com> <875yr1q8oa.fsf@redhat.com> <87o84qpk7d.fsf@redhat.com> <877dbbq5om.fsf@redhat.com> <5505d731-cf87-9662-33f3-08844d92877c@redhat.com> <20220111090022.1125ffb5@redhat.com> <87fsptnjic.fsf@redhat.com> <50136685-706e-fc6a-0a77-97e584e74f93@redhat.com> <87bl0gnfy5.fsf@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2022-01-13 at 10:27 +0100, Vitaly Kuznetsov wrote: > Paolo Bonzini writes: > > > On 1/12/22 14:58, Vitaly Kuznetsov wrote: > > > - best = kvm_find_cpuid_entry(vcpu, 0xD, 1); > > > + best = cpuid_entry2_find(entries, nent, 0xD, 1); > > > if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) || > > > cpuid_entry_has(best, X86_FEATURE_XSAVEC))) > > > best->ebx = xstate_required_size(vcpu->arch.xcr0, true); > > > > > > - best = kvm_find_kvm_cpuid_features(vcpu); > > > + best = __kvm_find_kvm_cpuid_features(vcpu, vcpu->arch.cpuid_entries, > > > + vcpu->arch.cpuid_nent); > > > if (kvm_hlt_in_guest(vcpu->kvm) && best && > > > > I think this should be __kvm_find_kvm_cpuid_features(vcpu, entries, nent). > > > > Of course. > > > > + case 0x1: > > > + /* Only initial LAPIC id is allowed to change */ > > > + if (e->eax ^ best->eax || ((e->ebx ^ best->ebx) >> 24) || > > > + e->ecx ^ best->ecx || e->edx ^ best->edx) > > > + return -EINVAL; > > > + break; > > > > This XOR is a bit weird. In addition the EBX test is checking the wrong > > bits (it checks whether 31:24 change and ignores changes to 23:0). > > Indeed, however, I've tested CPU hotplug with QEMU trying different > CPUs in random order and surprisingly othing blew up, feels like QEMU > was smart enough to re-use the right fd) > > > You can write just "(e->ebx & ~0xff000000u) != (best->ebx ~0xff000000u)". > > > > > + default: > > > + if (e->eax ^ best->eax || e->ebx ^ best->ebx || > > > + e->ecx ^ best->ecx || e->edx ^ best->edx) > > > + return -EINVAL; > > > > This one even more so. > > Thanks for the early review, I'm going to prepare a selftest and send > this out. > I also looked at this recently (due to other reasons) and I found out that qemu picks a parked vcpu by its vcpu_id which is its initial apic id, thus apic id related features should not change. Take a look at 'kvm_get_vcpu' in qemu source. Maybe old qemu versions didn't do this? Best regards, Thanks, Maxim Levitsky