Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v3] x86/speculation/l1tf: Add KConfig for setting the L1D
 cache flush mode
To:     Mike Rapoport <rppt@linux.ibm.com>,
        Doug Anderson <dianders@google.com>
Cc:     Abhishek Bhardwaj <abhishekbh@google.com>,
        Anthony Steinhauser <asteinhauser@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Mark Gross <mgross@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tony Luck <tony.luck@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>, kvm@vger.kernel.org,
        x86 <x86@kernel.org>
References: <20200702221237.2517080-1-abhishekbh@google.com>
 <e7bc00fc-fe53-800e-8439-f1fbdca5dd26@redhat.com>
 <CAN_oZf2t+gUqXe19Yo1mTzAgk2xNhssE-9p58EvH-gw5jpuvzA@mail.gmail.com>
 <CA+noqoj6u9n_KKohZw+QCpD-Qj0EgoCXaPEsryD7ABZ7QpqQfg@mail.gmail.com>
 <20200703114037.GD2999146@linux.ibm.com>
 <CAD=FV=XRbrFqSbR619h+9HXNyrYNbqfBF2e-+iUZco9qQ8Wokg@mail.gmail.com>
 <20200705152304.GE2999146@linux.ibm.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <5d2ccf3d-b473-cf30-b863-e29bb33b7284@redhat.com>
Date:   Sun, 5 Jul 2020 11:56:56 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.4.1
MIME-Version: 1.0
In-Reply-To: <20200705152304.GE2999146@linux.ibm.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 7/5/20 11:23 AM, Mike Rapoport wrote:
>> Nothing prevents people from continuing to use the command line
>> options if they want, right?  This just allows a different default.
>> So if a distro is security focused and decided that it wanted a slower
>> / more secure default then it could ship that way but individual users
>> could still override, right?
> Well, nothing prevents you from continuing to use the command line as
> well;-)
>
> I can see why whould you want an ability to select compile time default
> for an option, but I'm really not thrilled by the added ifdefery.
>   

It turns out that CONFIG_KVM_VMENTRY_L1D_FLUSH values match the enum 
vmx_l1d_flush_state values. So one way to reduce the ifdefery is to do, 
for example,

+#ifdef CONFIG_KVM_VMENTRY_L1D_FLUSH
+#define VMENTER_L1D_FLUSH_DEFAULT CONFIG_KVM_VMENTRY_L1D_FLUSH
+#else
+#define VMENTER_L1D_FLUSH_DEFAULT      VMENTER_L1D_FLUSH_AUTO
#endif
-enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_DEFAULT;

Of course, we may need to add a comment on enum vmx_l1d_flush_state 
definition to highlight the dependency of CONFIG_KVM_VMENTRY_L1D_FLUSH 
on it to avoid future mismatch.

Cheers,
Longman