From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to
 MSR_IA32_SPEC_CTRL
Date: Wed, 31 Jan 2018 16:42:58 -0500
Message-ID: <f6e76523-7727-6e79-7bcf-3d6c6ebd64d8@redhat.com>
References: <1517427467-28567-1-git-send-email-karahmed@amazon.de>
 <1517427467-28567-5-git-send-email-karahmed@amazon.de>
 <CALMp9eRgc-qKS5CDTvqoUDdnAXu8xqy9ZB-rew=P9NgE5AfXWA@mail.gmail.com>
 <06cb88da-f355-41ed-380f-7daa8ddf6159@amazon.com>
 <CALMp9eS9LAJz+u3ujKZ5kLHihHMZ68LHajn3ri7sRPPEgFbHfA@mail.gmail.com>
 <67dca2bb-1298-c7fa-f681-018e4edc6725@redhat.com>
 <CALMp9eT677DU=EGoezcyjRMAP3XKiK_6FBJb-rVQrBX2CSbTuw@mail.gmail.com>
 <16d89e09-fbfc-4a08-00a6-40cfb4776018@redhat.com>
 <CALMp9eQ5fbfnqCvs_dMhoTOGTDX-+yt6QtJdUfiQg1BXq-0P3A@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Cc: KarimAllah Ahmed <karahmed@amazon.com>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Ashok Raj <ashok.raj@intel.com>
To: Jim Mattson <jmattson@google.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <CALMp9eQ5fbfnqCvs_dMhoTOGTDX-+yt6QtJdUfiQg1BXq-0P3A@mail.gmail.com>
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

On 31/01/2018 16:05, Jim Mattson wrote:
> On Wed, Jan 31, 2018 at 1:00 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
>> Yes, but how would moving the field into struct loaded_vmcs do anything?
>>  Only vmon/vmoff would change anything in vmx->nested.vmcs02.
> 
> My suggestion was that nested_vmx_merge_msr_bitmap should set the
> vmcs02 version of save_spec_ctrl_on_exit based on the calculated value
> of the write permission bit for IA32_SPEC_CTRL in the vmcs02 MSR
> permission bitmap.
> 
>> Even then, L1 vmexits will also be penalized because L1 has probably
>> done an RDMSR/WRMSR on L2->L1 vmexit.  So I don't think it's an issue?
> 
> Yes, it sucks to be L1 in this situation.

Can we just say it sucks to be L2 too? :)  Because in the end as long as
no one ever writes to spec_ctrl, everybody is happy.

Paolo