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 119B2C433FE for ; Thu, 13 Jan 2022 16:30:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236715AbiAMQa6 (ORCPT ); Thu, 13 Jan 2022 11:30:58 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:38288 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236698AbiAMQa5 (ORCPT ); Thu, 13 Jan 2022 11:30:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642091455; 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=4H2G/AcFCWNIo4a7X3Hpex/LEo4UsnyCD4gzRSNQTAQ=; b=iS7qhr2ZU2Jf7Q/u02AJ/TnxnjtKJPDFFN4B6uGiWsvrdpSdxbtNZAOHgWTbP0uuxFfdo8 jYMedgFWvEUzQ3uoVJRTvR/D6EYLm+q3qehToo0vjKG/JD/PkzFv/lMaBmWiamFiQglO73 /jL/3ta2iN/v7MVaW8iSzU1lNpLYlgQ= 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-498-Ax1e_eeJPauRyoBTaav1KA-1; Thu, 13 Jan 2022 11:30:54 -0500 X-MC-Unique: Ax1e_eeJPauRyoBTaav1KA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4D54810AF8C2; Thu, 13 Jan 2022 16:30:53 +0000 (UTC) Received: from starship (unknown [10.40.192.177]) by smtp.corp.redhat.com (Postfix) with ESMTP id 95131858A0; Thu, 13 Jan 2022 16:30:50 +0000 (UTC) Message-ID: Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN From: Maxim Levitsky To: Sean Christopherson , Vitaly Kuznetsov Cc: Paolo Bonzini , Igor Mammedov , kvm@vger.kernel.org, Wanpeng Li , Jim Mattson , linux-kernel@vger.kernel.org Date: Thu, 13 Jan 2022 18:30:49 +0200 In-Reply-To: References: <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> <7e7c7e22f8b1b1695d26d9e19a767b87c679df93.camel@redhat.com> <87zgnzn1nr.fsf@redhat.com> <6ae7e64c53727f9f00537d787e9612c292c4e244.camel@redhat.com> <87wnj3n0k0.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 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2022-01-13 at 16:26 +0000, Sean Christopherson wrote: > On Thu, Jan 13, 2022, Vitaly Kuznetsov wrote: > > Maxim Levitsky writes: > > > For my nested AVIC work I would really want the APIC ID of a VCPU to be read-only > > > and be equal to vcpu_id. > > > > > > > Doesn't APIC ID have topology encoded in it? > > Yeah, APIC IDs are derived from the topology. From the SDM (this doesn't > talk about core/SMT info, but that's included as well): > > The hardware assigned APIC ID is based on system topology and includes encoding > for socket position and cluster information. > > The SDM also says: > > Some processors permit software to modify the APIC ID. However, the ability of > software to modify the APIC ID is processor model specific. > > So I _think_ we could define KVM behavior to ignore writes from the _guest_, but > the APIC_ID == vcpu_id requirement won't fly as userspace expects to be able to > stuff virtual toplogy info into the APIC ID. > That is a very good piece of information! Thanks! Best regards, Maxim Levitsky