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 2A621C433EF for ; Mon, 17 Jan 2022 13:02:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240090AbiAQNCi (ORCPT ); Mon, 17 Jan 2022 08:02:38 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:41557 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234253AbiAQNCg (ORCPT ); Mon, 17 Jan 2022 08:02:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1642424555; 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: in-reply-to:in-reply-to:references:references; bh=AmxLgMKtM2xp64rnq5p7GdtgJriOCMkjmIrcQ5U3IJY=; b=aVynspfbNhQ+xho5wYQtWHvuIN1vtHHV/vYs+84GM/JFAueca8AIDjEU822B3psrk40amp kspEFTOmuC47l3vpCIo+24pvcu/mcwN5FjqKgOzViaJft+hlKWjmAfx5/fUKnFqRj9YEth kpYcO5HADS/je73rDnhqvDgJqOkjgK0= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-349-6d7_BgZiM9KPizW97X4TAw-1; Mon, 17 Jan 2022 08:02:34 -0500 X-MC-Unique: 6d7_BgZiM9KPizW97X4TAw-1 Received: by mail-wm1-f69.google.com with SMTP id n13-20020a05600c3b8d00b0034979b7e200so5262687wms.4 for ; Mon, 17 Jan 2022 05:02:34 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=AmxLgMKtM2xp64rnq5p7GdtgJriOCMkjmIrcQ5U3IJY=; b=0XfMGgyG4hyI7mLE1jg0VJ5z0umpi7XFSgh8kFYCKNWmCzDcGluJHi4nBOxdn8qLS2 /UT0nv36JSVU1WwIU3S/DZyOufEZL1KH6UGylpA04K4DM9RLrmF7PwmES2UcyjsHQRe5 L5cNzLERbfFHwZe1zC02IZlWNh9e6HUj59mcYgQlT5gLi/z8Bhfq2qsw0qNv8pKaO4ch Zbr0rCQV3qDzoLp4uoqaGgqpvDTrU7LO7X8WoYI4mn+7SyEAYVKPGSyqLRb8E4XHIdWS H03RxydHGG0ONuyWZs7dhOtbB+gV5Pn/C3egjl9kWcX8kMwyioo6jA8XiH+V7aDzED5C YHWw== X-Gm-Message-State: AOAM532jWEuFJJuLfIVaF8CtQ7PZqoRc4TgUBLseeh+T2VaQMLSRs066 HosijxnnSOMWLmNNBydiGxAT75DtikoBxk/xDcVvkkOIcneEXEIdlIxrzQtGvawPJjjHzWT7htf t0LdRKUTB8gNc064goPClUVsMX2nRCjd5tUg1sWqN18dOr4V4W5C7qp02sg8bVfsiBFF5gGmYy/ ED X-Received: by 2002:a5d:5147:: with SMTP id u7mr13731050wrt.687.1642424553461; Mon, 17 Jan 2022 05:02:33 -0800 (PST) X-Google-Smtp-Source: ABdhPJw5gUyIT+6hmx9at0BIXTQZgqi8LBV9qiFylH3MqPMb8FTU5HuKtAntofElkn6GwInqCUKmTw== X-Received: by 2002:a5d:5147:: with SMTP id u7mr13730964wrt.687.1642424552481; Mon, 17 Jan 2022 05:02:32 -0800 (PST) Received: from fedora (nat-2.ign.cz. [91.219.240.2]) by smtp.gmail.com with ESMTPSA id az29sm9867067wmb.31.2022.01.17.05.02.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Jan 2022 05:02:31 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , Sean Christopherson Cc: Igor Mammedov , kvm@vger.kernel.org, Wanpeng Li , Jim Mattson , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN In-Reply-To: <517e8b95-e336-8796-6657-c0f8d554143a@redhat.com> References: <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> <20220114095535.0f498707@redhat.com> <87ilummznd.fsf@redhat.com> <20220114122237.54fa8c91@redhat.com> <87ee5amrmh.fsf@redhat.com> <8735lmn0t1.fsf@redhat.com> <517e8b95-e336-8796-6657-c0f8d554143a@redhat.com> Date: Mon, 17 Jan 2022 14:02:31 +0100 Message-ID: <87zgnuldlk.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 1/17/22 10:55, Vitaly Kuznetsov wrote: >> No, honestly I was thinking about something much simpler: instead of >> forbidding KVM_SET_CPUID{,2} after KVM_RUN completely (what we have now >> in 5.16), we only forbid to change certain data which we know breaks >> some assumptions in MMU, from the comment: >> " >> * KVM does not correctly handle changing guest CPUID after KVM_RUN, as >> * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't >> * tracked in kvm_mmu_page_role. As a result, KVM may miss guest page >> * faults due to reusing SPs/SPTEs. >> " >> It seems that CPU hotplug path doesn't need to change these so we don't >> need an opt-in/opt-out, we can just forbid changing certain things for >> the time being. Alternatively, we can silently ignore such changes but I >> don't quite like it because it would mask bugs in VMMs. > > I think the version that only allows exactly the same CPUID is the best, > as it leaves less room for future bugs. > Ok, I hear your vote) Will prepare v2. -- Vitaly