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 C7698C3526D for ; Wed, 26 Jan 2022 16:27:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243128AbiAZQ1P (ORCPT ); Wed, 26 Jan 2022 11:27:15 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55764 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236514AbiAZQ1N (ORCPT ); Wed, 26 Jan 2022 11:27:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643214432; 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=efzC2IwqGzejEAIdbekALVZEUqxrdpopAyww58idfp8=; b=SA+donqYp+rAoMJ4gISW//JCe04SN8W3z750NY052iDabqcaZtR+DdZf0EhqhkAUZgWf2q FpVNITOfcb6PtCi2sh+QrhHHTTr/go5iKBLSaLzQpdxZhopYgPh77jywCsxh8XKCxbZHAI sTRFSWhci189IqwoCDCnI0qjU0bjXcA= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-340-BoJLihVLPmqdv4crEgUq8g-1; Wed, 26 Jan 2022 11:27:11 -0500 X-MC-Unique: BoJLihVLPmqdv4crEgUq8g-1 Received: by mail-wm1-f71.google.com with SMTP id q125-20020a1c4383000000b003503e10c027so841wma.2 for ; Wed, 26 Jan 2022 08:27:10 -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=efzC2IwqGzejEAIdbekALVZEUqxrdpopAyww58idfp8=; b=XDs0i4boubk7GkSHRnlEUpdYPbN5pxYT/r3uMKYa2UtEpVIl6L+4sKZmO0P90ljPDU 2DenpX3GGrRRH+Un8uAzaXzNbsNC2oMOowMt817MWXO7I3PPlnD/OMWTD9KJIIIqaOH4 nob2ceA0j/ZPzVN8rmUHqC166bHqLpqK2W/HlA58OI4qbTTYEBQ/v8qiXcGCQUuXywD0 663UUw7ICyymJiY/J66zf7neOIGDxIA5o16g5lPX5JDCz30e28Mq2jx+Pwg0fH9HFG6W /KAKPCKEUKCFLrBE/tObpip5hueDoqPnylljFXJu9egD+IwiD+Mbha94ZMbRS/v2S9LU +XLw== X-Gm-Message-State: AOAM532gG3L6wHJNTL0SkBeKa7WIePYe85gfJmQNuke837XizugZg4CO A3TrLolvVcQLgqHRQAOvR8j9lHsNEAJOrrxjiEnNivoZVA2P0eyiVhm1cc/GNjutZC/S/qAaKYT 8fwo4yFz1+eAP/j2CeqAQkWNJtoaOney8JfRv8uruJXatTscgNlHqGqK5a2ce8cWqEFJ5t++6cK wQ X-Received: by 2002:a7b:c08b:: with SMTP id r11mr8062085wmh.111.1643214429942; Wed, 26 Jan 2022 08:27:09 -0800 (PST) X-Google-Smtp-Source: ABdhPJzat5xFG+n6X0ZtwIT2WzJvrNYAslBIVDm2zn1aj/rH3RM3gfE4afk84ck3WLdB4s/rkdFzNA== X-Received: by 2002:a7b:c08b:: with SMTP id r11mr8062061wmh.111.1643214429639; Wed, 26 Jan 2022 08:27:09 -0800 (PST) Received: from fedora (nat-2.ign.cz. [91.219.240.2]) by smtp.gmail.com with ESMTPSA id a14sm21852909wri.25.2022.01.26.08.27.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jan 2022 08:27:09 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , Sean Christopherson Cc: Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: nVMX: WARN on any attempt to allocate shadow VMCS for vmcs02 In-Reply-To: <053bb241-ea71-abf8-262b-7b452dc49d37@redhat.com> References: <20220125220527.2093146-1-seanjc@google.com> <87r18uh4of.fsf@redhat.com> <053bb241-ea71-abf8-262b-7b452dc49d37@redhat.com> Date: Wed, 26 Jan 2022 17:27:08 +0100 Message-ID: <87k0emh38j.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 1/26/22 16:56, Vitaly Kuznetsov wrote: >>> - WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs); >>> + if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs)) >>> + return loaded_vmcs->shadow_vmcs; >> Stupid question: why do we want to care about 'loaded_vmcs' at all, >> i.e. why can't we hardcode 'vmx->vmcs01' in alloc_shadow_vmcs()? The >> only caller is enter_vmx_operation() and AFAIU 'loaded_vmcs' will always >> be pointing to 'vmx->vmcs01' (as enter_vmx_operation() allocates >> &vmx->nested.vmcs02 so 'loaded_vmcs' can't point there!). >> > > Well, that's why the WARN never happens. The idea is that if shadow > VMCS _virtualization_ (not emulation, i.e. running L2 VMREAD/VMWRITE > without even a vmexit to L0) was supported, then you would need a > non-NULL shadow_vmcs in vmx->vmcs02. > > Regarding the patch, the old WARN was messy but it was also trying to > avoid a NULL pointer dereference in the caller. > > What about: > > if (WARN_ON(loaded_vmcs->shadow_vmcs)) > return loaded_vmcs->shadow_vmcs; > > /* Go ahead anyway. */ > WARN_ON(loaded_vmcs != &vmx->vmcs01); > > ? > FWIW, this looks better [to my personal taste]. -- Vitaly